Putting it all together-Neural integration Muse lecture #16 Ch 15-16.

Putting it all together-Neural integration

Muse lecture #16Ch 15-16

Sensory Information

Afferent Division of the Nervous System

Receptors

Sensory neurons

Sensory pathways

Efferent Division of the Nervous System

Nuclei

Motor tracts

Motor neurons

Sensory Information

Figure 15–1 An Overview of Neural Integration.

Sensory Information

Somatic Nervous System (SNS)

Motor neurons and pathways that control

skeletal muscles

Sensory Receptors

Sensation

The arriving information from these senses

Perception

Conscious awareness of a sensation

Sensory Receptors

Special Senses

Olfaction (smell)

Vision (sight)

Gustation (taste)

Equilibrium (balance)

Hearing

Sensory Receptors

The Detection of Stimuli

Receptor sensitivity

Each receptor has a characteristic sensitivity

Receptive field

Area is monitored by a single receptor cell

The larger the receptive field, the more difficult it is

to localize a stimulus

Sensory Receptors

Figure 15–2 Receptors and Receptive Fields

Sensory Receptors

The Interpretation of Sensory Information

Arriving stimulus

Takes many forms:

– physical force (such as pressure)

– dissolved chemical

– sound

– light

Sensory Receptors

The Interpretation of Sensory Information

Sensations

Taste, hearing, equilibrium, and vision provided by

specialized receptor cells

Communicate with sensory neurons across

chemical synapses

Sensory Receptors

Adaptation

Reduction in sensitivity of a constant stimulus

Your nervous system quickly adapts to stimuli

that are painless and constant example smell

Sensory Receptors

Adaptation

Tonic receptors

Are always active

Show little peripheral adaptation

Are slow-adapting receptors

Remind you of an injury long after the initial

damage has occurred

Sensory Receptors

Adaptation

Phasic receptors

Are normally inactive

Become active for a short time whenever a change

occurs

Provide information about the intensity and rate of

change of a stimulus

Are fast-adapting receptors

Sensory Receptors

Stimulation of a receptor produces action potentials

along the axon of a sensory neuron

The frequency and pattern of action potentials

contain information about the strength, duration, and

variation of the stimulus

Your perception of the nature of that stimulus

depends on the path it takes inside the CNS

Classifying Sensory Receptors

Exteroceptors provide information about

the external environment

Proprioceptors report the positions of

skeletal muscles and joints

Interoceptors monitor visceral organs and

functions


Proprioceptors

Provide a purely somatic sensation

No proprioceptors in the visceral organs of the

thoracic and abdominopelvic cavities

You cannot tell where your spleen, appendix, or

pancreas is at the moment


General sensory receptors are divided into

four types by the nature of the stimulus that

excites them

Nociceptors (pain)

Thermoreceptors (temperature)

Mechanoreceptors (physical distortion)

Chemoreceptors (chemical concentration)


Nociceptors (also called pain receptors)

Are common in the superficial portions of the

skin, joint capsules, within the periostea of

bones, and around the walls of blood vessels

May be sensitive to temperature extremes,

mechanical damage, and dissolved chemicals,

such as chemicals released by injured cells

Figure 15–2


Nociceptors

Are free nerve endings with large receptive

fields

Branching tips of dendrites

Not protected by accessory structures

Can be stimulated by many different stimuli

Two types of axons: Type A and Type C fibers


Nociceptors

Myelinated Type A fibers

Carry sensations of fast pain, or prickling pain,

such as that caused by an injection or a deep cut

Sensations reach the CNS quickly and often

trigger somatic reflexes

Relayed to the primary sensory cortex and receive

conscious attention


Nociceptors

Type C fibers

Carry sensations of slow pain, or burning and

aching pain

Cause a generalized activation of the reticular

formation and thalamus

You become aware of the pain but only have a

general idea of the area affected


Thermoreceptors

Also called temperature receptors

Are free nerve endings located in

The dermis

Skeletal muscles

The liver

The hypothalamus


Thermoreceptors

Temperature sensations

Conducted along the same pathways that carry

pain sensations

Sent to:

– the reticular formation

– the thalamus

– the primary sensory cortex (to a lesser extent)


Mechanoreceptors

Sensitive to stimuli that distort their plasma membranes

Contain mechanically gated ion channels whose gates

open or close in response to

Stretching

Compression

Twisting

Other distortions of the membrane


Three Classes of Mechanoreceptors Tactile receptors

provide the sensations of touch, pressure, and vibration:

– touch sensations provide information about shape or texture

– pressure sensations indicate degree of mechanical distortion

– vibration sensations indicate pulsing or oscillating pressure


Three Classes of Mechanoreceptors

Baroreceptors

Detect pressure changes in the walls of

blood vessels and in portions of the

digestive, reproductive, and urinary tracts


Three Classes of Mechanoreceptors

Proprioceptors

Monitor the positions of joints and muscles

The most structurally and functionally

complex of general sensory receptors


Mechanoreceptors: Tactile Receptors

Fine touch and pressure receptors

Are extremely sensitive

Have a relatively narrow receptive field

Provide detailed information about a source of

stimulation, including:

– its exact location, shape, size, texture, movement


Mechanoreceptors: Tactile Receptors

Crude touch and pressure receptors

Have relatively large receptive fields

Provide poor localization

Give little information about the stimulus


Six Types of Tactile Receptors in the Skin

1. Free nerve endings

Sensitive to touch and pressure

Situated between epidermal cells

Free nerve endings providing touch sensations are tonic

receptors with small receptive fields


Figure 15–3a Tactile Receptors in the Skin.

1.

2.

3.

4

5. 6

Figure 15–3b


Six Types of Tactile Receptors in the Skin

2. Root hair plexus nerve endings rapid

• 3. Tactile discs tonicAlso called Merkel discs

Fine touch and pressure receptors

Extremely sensitive to tonic receptors

Have very small receptive fields


Figure 15–3b Tactile Receptors in the Skin.

Figure 15–3d

Classifying Sensory Receptors 4. Tactile corpuscles: rapid

Also called Meissner corpuscles

Perceive sensations of fine touch, pressure, and low-

frequency vibration

Adapt to stimulation within 1 second after contact

Most abundant in the eyelids, lips, fingertips, nipples, and

external genitalia

5. Lamellated corpuscles (Pacinian) rapidSensitive to deep pressure

Fast-adapting receptors

Most sensitive to pulsing or high-frequency vibrating stimuli


Figure 15–3d Tactile Receptors in the Skin.

Figure 15–3f


6 Ruffini corpuscles tonic

Also sensitive to pressure and distortion of the

skin

Located in the reticular (deep) dermis

Tonic receptors that show little if any adaptation


Figure 15–3f Tactile Receptors in the Skin.


Baroreceptors

Monitor change in pressure

Consist of free nerve endings that branch

within elastic tissues in wall of distensible

organ (such as a blood vessel)

Respond immediately to a change in

pressure, but adapt rapidly


Proprioceptors

Monitor

Position of joints

Tension in tendons and ligaments

State of muscular contraction


Three Major Groups of Proprioceptors

Muscle spindles

Monitor skeletal muscle length

Trigger stretch reflexes

Golgi tendon organs

Located at the junction between skeletal muscle and its tendon

Stimulated by tension in tendon

Monitor external tension developed during muscle contraction

Receptors in joint capsules

Free nerve endings detect pressure, tension, movement at the joint


Chemoreceptors

Respond only to water-soluble and lipid-

soluble substances dissolved in surrounding

fluid

Receptors exhibit peripheral adaptation over

period of seconds; central adaptation may

also occur

Sensory Pathways

First-Order Neuron

Sensory neuron delivers sensations to the CNS

Cell body of a first-order general sensory neuron is located in dorsal

root ganglion or cranial nerve ganglion

Second-Order Neuron

Axon of the sensory neuron synapses on an interneuron in the CNS

May be located in the spinal cord or brain stem

Third-Order Neuron

If the sensation is to reach our awareness, the second-order neuron

synapses on a third-order neuron in the thalamus

Sensory Pathways

Somatic Sensory Pathways

Carry sensory information from the skin and

musculature of the body wall, head, neck, and limbs

Three major somatic sensory pathways

1 The posterior column pathway

2 The spinothalamic pathway

3 The spinocerebellar pathway

Sensory Pathways

Figure 15–4 Sensory Pathways and Ascending Tracts in the Spinal Cord.

3

1

2

Sensory Pathways

Somatic Sensory Pathways

Posterior column pathway

Carries sensations of highly localized (“fine”)

touch, pressure, vibration, and proprioception

Spinal tracts involved:

– left and right fasciculus gracilis

– left and right fasciculus cuneatus

Figure 15–5a

Sensory Pathways

Posterior Column Pathway

Axons synapse

On third-order neurons in one of the ventral nuclei

of the thalamus

Nuclei sort the arriving information according to:

– the nature of the stimulus

– the region of the body involved

Figure 15–5a

Sensory Pathways


Processing in the thalamus

Determines whether you perceive a given sensation as fine

touch, as pressure, or as vibration

Ability to determine stimulus

Precisely where on the body a specific stimulus originated

depends on the projection of information from the thalamus

to the primary sensory cortex

Figure 15–5a

Sensory Pathways


Sensory information

From toes arrives at one end of the primary

sensory cortex

From the head arrives at the other:

– when neurons in one portion of your primary sensory

cortex are stimulated, you become aware of sensations

originating at a specific location

Figure 15–5a

Sensory Pathways


Sensory homunculus

Functional map of the primary sensory cortex

Distortions occur because area of sensory cortex

devoted to particular body region is not

proportional to region’s size, but to number of

sensory receptors it contains

Sensory Pathways

Figure 15–5a The Posterior Column Pathway.

Sensory Pathways

The Spinothalamic Pathway

Provides conscious sensations of poorly localized

(“crude”) touch, pressure, pain, and temperature

First-order neurons

Axons of first-order sensory neurons enter spinal cord and

synapse on second-order neurons within posterior gray

horns

Sensory Pathways


Second-order neurons

Cross to the opposite side of the spinal cord before

ascending

Ascend within the anterior or lateral spinothalamic

tracts:

– the anterior tracts carry crude touch and pressure

sensations

– the lateral tracts carry pain and temperature sensations

Sensory Pathways


Third-order neurons

Synapse in ventral nucleus group of the thalamus

After the sensations have been sorted and

processed, they are relayed to primary sensory

cortex

Sensory Pathways

Figure 15–5b The Spinothalamic Tracts of the Spinothalamic Pathway.

Sensory Pathways

Figure 15–5c The Spinothalamic Tracts of the Spinothalamic Pathway.

humunculus

Sensory Pathways

Feeling Pain (Lateral Spinothalamic Tract)

An individual can feel pain in an uninjured part of the

body when pain actually originates at another location

Strong visceral pain

Sensations arriving at segment of spinal cord can stimulate

interneurons that are part of spinothalamic pathway

Activity in interneurons leads to stimulation of primary

sensory cortex, so an individual feels pain in specific part of

body surface:

– also called referred pain

Sensory Pathways

Figure 15–6 Referred Pain.

Sensory Pathways

The Spinocerebellar Pathway

Cerebellum receives proprioceptive

information about position of skeletal

muscles, tendons, and joints

Figure 15–7

Sensory Pathways

The Spinocerebellar Tracts

The posterior spinocerebellar tracts

Contain second-order axons that do NOT cross

over to the opposite side of the spinal cord:

– axons reach cerebellar cortex via inferior cerebellar

peduncle of that side

Sensory Pathways

Figure 15–7 The Spinocerebellar Pathway.

Sensory Pathways

Sensory Pathways

Most somatic sensory information is

relayed to the thalamus for processing

A small fraction of the arriving information

is projected to the cerebral cortex and

reaches our awareness

Sensory Pathways

Visceral Sensory Pathways

Collected by interoceptors monitoring visceral

tissues and organs, primarily within the thoracic and

abdominopelvic cavities

These interoceptors are not as numerous as in

somatic tissues

Nociceptors, thermoreceptors, tactile receptors,

baroreceptors, and chemoreceptors

Sensory Pathways


Cranial Nerves V, VII, IX, and X

Carry visceral sensory information from mouth,

palate, pharynx, larynx, trachea, esophagus, and

associated vessels and glands

Sensory Pathways


Solitary nucleus

Large nucleus in the medulla oblongata

Major processing and sorting center for visceral

sensory information

Extensive connections with the various

cardiovascular and respiratory centers, reticular

formation

Somatic Motor Pathways

SNS, or the somatic motor system, controls

contractions of skeletal muscles (discussed

next)

ANS, or the visceral motor system, controls

visceral effectors, such as smooth muscle,

cardiac muscle, and glands (Ch. 16)


Always involve at least two motor neurons

1 Upper motor neuron

Cell body lies in a CNS processing center

Synapses on the lower motor neuron

Innervates a single motor unit in a skeletal muscle:

– activity in upper motor neuron may facilitate or inhibit

lower motor neuron


2 Lower motor neuron

Cell body lies in a nucleus of the brain stem or

spinal cord

Triggers a contraction in innervated muscle:

– only axon of lower motor neuron extends outside CNS

– destruction of or damage to lower motor neuron

eliminates voluntary and reflex control over innervated

motor unit


Conscious and Subconscious Motor

Commands

Control skeletal muscles by traveling over

three integrated motor pathways

Corticospinal pathway

Medial pathway

Lateral pathway


Figure 15–8 Descending (Motor) Tracts in the Spinal Cord.


The Corticospinal Pathway Sometimes called the pyramidal system

Provides voluntary control over skeletal muscles System begins at pyramidal cells of primary motor cortex

Axons of these upper motor neurons descend into brain stem

and spinal cord to synapse on lower motor neurons that

control skeletal muscles

Contains three pairs of descending tracts Corticobulbar tracts

Lateral corticospinal tracts

Anterior corticospinal tracts


The Corticospinal Pathway

Corticobulbar tracts

Provide conscious control over skeletal muscles

that move the eye, jaw, face, and some muscles of

neck and pharynx

Innervate motor centers of medial and lateral

pathways


The Corticospinal Pathway Corticospinal tracts

As they descend, lateral corticospinal tracts are visible

along the ventral surface of medulla oblongata as pair of

thick bands, the pyramids

At spinal segment it targets, an axon in anterior

corticospinal tract crosses over to opposite side of spinal

cord in anterior white commissure before synapsing on

lower motor neurons in anterior gray horns


The Corticospinal Pathway Motor homunculus

Primary motor cortex corresponds point by point with specific

regions of the body

Cortical areas have been mapped out in diagrammatic form

Homunculus provides indication of degree of fine motor

control available:

– hands, face, and tongue, which are capable of varied and

complex movements, appear very large, while trunk is relatively

small

– these proportions are similar to the sensory homunculus


Figure 15–9 The Corticospinal Pathway.


The Medial and Lateral Pathways

Several centers in cerebrum, diencephalon, and brain

stem may issue somatic motor commands as result of

processing performed at subconscious level

These nuclei and tracts are grouped by their primary

functions

Components of medial pathway help control gross

movements of trunk and proximal limb muscles

Components of lateral pathway help control distal limb

muscles that perform more precise movements


The Medial Pathway

Primarily concerned with control of muscle tone and

gross movements of neck, trunk, and proximal limb

muscles

Upper motor neurons of medial pathway are located

in

Vestibular nuclei

Superior and inferior colliculi

Reticular formation


The Medial Pathway

Vestibular nuclei

Receive information over the vestibulocochlear

nerve (VIII) from receptors in inner ear that monitor

position and movement of the head:

– primary goal is to maintain posture and balance

– descending fibers of spinal cord constitute

vestibulospinal tracts


The Medial Pathway

Superior and inferior colliculi

Are located in the roof of the mesencephalon, or the tectum

Colliculi receive visual (superior) and auditory (inferior)

sensations

Axons of upper motor neurons in colliculi descend in

tectospinal tracts

These axons cross to opposite side, before descending to

synapse on lower motor neurons in brain stem or spinal cord


The Medial Pathway

Reticular formation

Loosely organized network of neurons that extends

throughout brain stem

Axons of upper motor neurons in reticular

formation descend into reticulospinal tracts

without crossing to opposite side


The Lateral Pathway

Primarily concerned with control of muscle

tone and more precise movements of distal

parts of limbs:

axons of upper motor neurons in red nuclei

cross to opposite side of brain and descend

into spinal cord in rubrospinal tracts




The Basal Nuclei and Cerebellum

Responsible for coordination and feedback

control over muscle contractions, whether

contractions are consciously or

subconsciously directed


The Basal Nuclei

Provide background patterns of movement involved in

voluntary motor activities

Some axons extend to the premotor cortex, the motor

association area that directs activities of the primary motor

cortex:

– alters the pattern of instructions carried by the corticospinal

tracts

Other axons alter the excitatory or inhibitory output of the

reticulospinal tracts


The Cerebellum

Monitors

Proprioceptive (position) sensations

Visual information from the eyes

Vestibular (balance) sensations from inner ear as

movements are under way


Levels of Processing and Motor Control

All sensory and motor pathways involve a series of synapses,

one after the other

General pattern

Spinal and cranial reflexes provide rapid, involuntary,

preprogrammed responses that preserve homeostasis over short

term

Cranial and spinal reflexes

Control the most basic motor activities


Levels of Processing and Motor Control

Integrative centers in the brain

Perform more elaborate processing

As we move from medulla oblongata to cerebral cortex,

motor patterns become increasingly complex and variable

Primary motor cortex

Most complex and variable motor activities are directed by

primary motor cortex of cerebral hemispheres


Neurons of the primary motor cortex innervate

motor neurons in the brain and spinal cord

responsible for stimulating skeletal muscles

Higher centers in the brain can suppress or

facilitate reflex responses

Reflexes can complement or increase the

complexity of voluntary movements

An Introduction to the ANS

Somatic Nervous System (SNS) Operates under conscious control

Seldom affects long-term survival

SNS controls skeletal muscles

Autonomic Nervous System (ANS) Operates without conscious instruction

ANS controls visceral effectors

Coordinates system functions: cardiovascular, respiratory,

digestive, urinary, reproductive

Autonomic Nervous System

Organization of the ANS

Integrative centers

For autonomic activity in hypothalamus

Neurons comparable to upper motor neurons in

SNS


Organization of the ANS

Visceral motor neurons

In brain stem and spinal cord, are known as

preganglionic neurons

Preganglionic fibers:

– axons of preganglionic neurons

– leave CNS and synapse on ganglionic neurons


Visceral Motor Neurons (cont’d)

Autonomic ganglia

Contain many ganglionic neurons

Ganglionic neurons innervate visceral effectors:

– such as cardiac muscle, smooth muscle, glands, and

adipose tissue

Postganglionic fibers:

– axons of ganglionic neurons


Figure 16-2a The Organization of the Somatic and Nervous Systems.


Figure 16-2b The Organization of the Autonomic Nervous Systems.

Divisions of the ANS

The autonomic nervous system

Operates largely outside our awareness

Has two divisions

Sympathetic division gas pedal

– increases alertness, metabolic rate, and muscular

abilities fight or flight

Parasympathetic division brake

– reduces metabolic rate and promotes digestion

Rest and digest


Two divisions may work independently

Some structures innervated by only one

division

Two divisions may work together

Each controlling one stage of a complex

process


Sympathetic Division

Preganglionic fibers (thoracic and superior lumbar;

thoracolumbar) synapse in ganglia near spinal cord

Preganglionic fibers are short

Postganglionic fibers are long

Prepares body for crisis, producing a “fight or flight”

response

Stimulates tissue metabolism

Increases alertness


Seven Responses to Increased Sympathetic Activity

Heightened mental alertness

Increased metabolic rate

Reduced digestive and urinary functions

Energy reserves activated

Increased respiratory rate and respiratory passageways dilate

Increased heart rate and blood pressure

Sweat glands activated


Parasympathetic Division

Preganglionic fibers originate in brain stem and sacral

segments of spinal cord; craniosacral

Synapse in ganglia close to (or within) target organs

Preganglionic fibers are long

Postganglionic fibers are short


Parasympathetic Division

Rest and repose

Parasympathetic division stimulates visceral activity

Conserves energy and promotes sedentary activities

Decreased metabolic rate, heart rate, and blood pressure

Increased salivary and digestive glands secretion

Increased motility and blood flow in digestive tract

Urination and defecation stimulation


Enteric Nervous System (ENS)

Third division of ANS

Extensive network in digestive tract walls

Complex visceral reflexes coordinated locally

Roughly 100 million neurons

All neurotransmitters are found in the brain

The Sympathetic Division

Preganglionic neurons located between

segments T1 and L2 of spinal cord

Ganglionic neurons in ganglia near vertebral

column

Cell bodies of preganglionic neurons in lateral

gray horns

Axons enter ventral roots of segments


Figure 16–3 The Organization of the Sympathetic Division of the ANS.


Ganglionic Neurons

Occur in three locations

Sympathetic chain ganglia

Collateral ganglia

Suprarenal medullae


Figure 16–4a Sites of Ganglia in Sympathetic Pathways


Figure 16–4b Sites of Ganglia in Sympathetic Pathways.


Figure 16–4c Sites of Ganglia in Sympathetic Pathways.


Fibers in Sympathetic Division

Preganglionic fibers

Are relatively short

Ganglia located near spinal cord

Postganglionic fibers

Are relatively long, except at suprarenal medullae

Various Sympathetic Neurotransmitters

Sympathetic Stimulation and the Release

of ACh and NO

Cholinergic (ACh) sympathetic terminals

Innervate sweat glands of skin and blood vessels

of skeletal muscles and brain

Stimulate sweat gland secretion and dilate blood

vessels

Various Sympathetic Neurotransmitters

Sympathetic Stimulation and the Release

of ACh and NO

Nitroxidergic synapses

Release nitric oxide (NO) as neurotransmitter

Neurons innervate smooth muscles in walls of

blood vessels in skeletal muscles and the brain

Produce vasodilation and increased blood flow

The Parasympathetic Division

Autonomic Nuclei

Are contained in the mesencephalon, pons,

and medulla oblongata

associated with cranial nerves III, VII, IX, X

In lateral gray horns of spinal segments S2–S4

Organization and Anatomy of the Parasympathetic Division

Figure 16–7 The Organization of the Parasympathetic Division of the ANS.


Figure 16–8 The Distribution of Parasympathetic Innervation.


Figure 16–8 The Distribution of Parasympathetic Innervation.


Parasympathetic Activation

Centers on relaxation, food processing, and

energy absorption

Localized effects, last a few seconds at most


Major effects of parasympathetic division include

Constriction of pupils

Restricts light entering eyes

Secretion by digestive glands

Exocrine and endocrine

Secretion of hormones

Nutrient absorption and utilization

Changes in blood flow and glandular activity

Associated with sexual arousal

Parasympathetic Neurons Release ACh

Neuromuscular and Neuroglandular Junctions

All release ACh as neurotransmitter

Small, with narrow synaptic clefts

Effects of stimulation are short lived

Inactivated by AChE at synapse

ACh is also inactivated by pseudocholinesterase (tissue

cholinesterase) in surrounding tissues


Membrane Receptors and Responses

Nicotinic receptors

On surfaces of ganglion cells (sympathetic and

parasympathetic):

– exposure to ACh causes excitation of ganglionic neuron

or muscle fiber


Dual Innervation

Sympathetic

Widespread impact

Reaches organs and tissues throughout body

Parasympathetic

Innervates only specific visceral structures

Most vital organs receive instructions from both

sympathetic and parasympathetic divisions

Two divisions commonly have opposing effects

Dual Innervation

Anatomy of Dual Innervation

Parasympathetic postganglionic fibers

accompany cranial nerves to peripheral

destinations

Sympathetic innervation reaches same

structures by traveling directly from superior

cervical ganglia of sympathetic chain

Dual Innervation

Figure 16–9 Summary: The Anatomical Differences between theSympathetic and Parasympathetic Divisions.

Anatomy of Dual Innervation

Figure 16–10 The Autonomic Plexuses.

Dual Innervation

The heart receives dual innervation

Two divisions have opposing effects Parasympathetic division

Acetylcholine released by postganglionic fibers slows heart rate

Sympathetic division NE released by varicosities accelerates heart rate

Balance between two divisions Autonomic tone is present

Releases small amounts of both neurotransmitters continuously

Dual Innervation

The heart receives dual innervation

Parasympathetic innervation dominates under

resting conditions

Crisis accelerates heart rate by

Stimulation of sympathetic innervation

Inhibition of parasympathetic innervation

Visceral Reflexes Regulate Autonomic Function

Figure 16–12 A Comparison of Somatic and Autonomic Function.

Higher-Order Functions

Require the cerebral cortex

Involve conscious and unconscious

information processing

Not part of programmed “wiring” of brain

Can adjust over time


Memory Fact memories

Are specific bits of information

Skill memories Learned motor behaviors

Incorporated at unconscious level with repetition

Programmed behaviors stored in appropriate area of brain

stem

Complex are stored and involve motor patterns in the basal

nuclei, cerebral cortex, and cerebellum


Memory

Short–term memories

Information that can be recalled immediately

Contain small bits of information

Primary memories

Long-term memories

Memory consolidation: conversion from short-term to long-

term memory:

– secondary memories fade and require effort to recall

– tertiary memories are with you for life


Figure 16–13 Memory Storage.

The limbic system


Brain Regions Involved in Memory Consolidation

and Access

Amygdaloid body and hippocampus

Nucleus basalis

Cerebral cortex

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

memory


Amygdaloid body and hippocampus

Are essential to memory consolidation

Damage may cause

Inability to convert short-term memories to new

long-term memories

Existing long-term memories remain intact and

accessible

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

memory


Nucleus Basalis

Cerebral nucleus near diencephalon

Plays uncertain role in memory storage and retrieval

Tracts connect with hippocampus, amygdaloid body,

and cerebral cortex

Damage changes emotional states, memory, and

intellectual functions


Cerebral cortex Stores long-term memories

Conscious motor and sensory memories referred to

association areas

Occipital and temporal lobes Special portions crucial to memories of faces, voices, and

words

A specific neuron may be activated by combination of

sensory stimuli associated with particular individual; called

“grandmother cells”


Cerebral cortex

Visual association area

Auditory association area

Speech center

Frontal lobes

Related information stored in other locations

If storage area is damaged, memory will be incomplete


Cellular Mechanisms of Memory Formation and

Storage

Involves anatomical and physiological

changes in neurons and synapses

Increased neurotransmitter release

Facilitation at synapses

Formation of additional synaptic connections


Increased Neurotransmitter Release

Frequently active synapse increases the

amount of neurotransmitter it stores

Releases more on each stimulation

The more neurotransmitter released, the

greater effect on postsynaptic neuron


Facilitation at Synapses Neural circuit repeatedly activated

Synaptic terminals begin continuously releasing

neurotransmitter

Neurotransmitter binds to receptors on postsynaptic

membrane

Produces graded depolarization

Brings membrane closer to threshold

Facilitation results affect all neurons in circuit


Formation of Additional Synaptic Connections

Neurons repeatedly communicating

Axon tip branches and forms additional synapses on

postsynaptic neuron

Presynaptic neuron has greater effect on

transmembrane potential of postsynaptic neuron



Storage

Basis of memory storage

Processes create anatomical changes

Facilitate communication along specific neural circuit

Memory Engram

Single circuit corresponds to single memory

Forms as result of experience and repetition



Storage

Efficient conversion of short-term memory

Takes at least 1 hour

Repetition crucial

Factors of conversion

Nature, intensity, and frequency of original stimulus

Strong, repeated, and exceedingly pleasant or unpleasant

events likely converted to long-term memories


Cellular Mechanisms of Memory Formation and Storage Drugs stimulate CNS

Caffeine and nicotine are examples:– enhance memory consolidation through facilitation

NMDA (N-methyl D-aspartate) Receptors:– linked to consolidation– chemically gated calcium channels– activated by neurotransmitter glycine– gates open, calcium enters cell– blocking NMDA receptors in hippocampus prevents long-

term memory formation


States of Consciousness

Many gradations of states

Degree of wakefulness indicates level of

ongoing CNS activity

When abnormal or depressed, state of

wakefulness is affected



Deep sleep

Also called slow-wave sleep

Entire body relaxes

Cerebral cortex activity minimal

Heart rate, blood pressure, respiratory rate, and

energy utilization decline up to 30%



Rapid eye movement (REM) sleep

Active dreaming occurs

Changes in blood pressure and respiratory rate

Less receptive to outside stimuli than in deep sleep

Muscle tone decreases markedly

Intense inhibition of somatic motor neurons

Eyes move rapidly as dream events unfold



Nighttime sleep pattern

Alternates between levels

Begins in deep sleep

REM periods average 5 minutes in length;

increase to 20 minutes over 8 hours


Sleep

Has important impact on CNS

Produces only minor changes in physiological

activities of organs and systems

Protein synthesis in neurons increases during sleep

Extended periods without sleep lead to disturbances

in mental function 25% of U.S. population experiences sleep disorders


Figure 16–14 Levels of Sleep.



Arousal and the reticular activating system (RAS)

Awakening from sleep

Function of reticular formation:

– extensive interconnections with sensory, motor, integrative nuclei,

and pathways along brain stem

Determined by complex interactions between reticular formation

and cerebral cortex


Reticular Activating System (RAS) Important brain stem component

Diffuse network in reticular formation

Extends from medulla oblongata to mesencephalon

Output of RAS projects to thalamic nuclei that

influence large areas of cerebral cortex

When RAS inactive, so is cerebral cortex

Stimulation of RAS produces widespread activation

of cerebral cortex


Arousal and the Reticular Activating

System

Ending sleep

Any stimulus activates reticular formation and RAS

Arousal occurs rapidly

Effects of single stimulation of RAS last less than a

minute


Arousal and the Reticular Activating System

Maintaining consciousness

Activity in cerebral cortex, basal nuclei, and sensory and

motor pathways continue to stimulate RAS:

– after many hours, reticular formation becomes less responsive

to stimulation

– individual becomes less alert and more lethargic

– neural fatigue reduces RAS activity


Arousal and the Reticular Activating System

Regulation of awake–asleep cycles

Involves interplay between brain stem nuclei that use

different neurotransmitters

Group of nuclei stimulates RAS with NE and maintains

awake, alert state

Other group promotes deep sleep by depressing RAS

activity with serotonin

“Dueling” nuclei located in brain stem


Figure 16–15 The Reticular Activating System.

Brain Chemistry

Huntington Disease

Destruction of ACh-secreting and GABA-secreting

neurons in basal nuclei

Symptoms appear as basal nuclei and frontal lobes

slowly degenerate

Difficulty controlling movements

Intellectual abilities gradually decline

Brain Chemistry

Lysergic Acid Diethylamide (LSD)

Powerful hallucinogenic drug

Activates serotonin receptors in brain stem,

hypothalamus, and limbic system

Brain Chemistry

Serotonin

Compounds that enhance effects also

produce hallucinations (LSD)

Compounds that inhibit or block action cause

severe depression and anxiety

Variations in levels affect sensory

interpretation and emotional states

Brain Chemistry

Serotonin

Fluoxetine (Prozac) Slows removal of serotonin at synapses

Increases serotonin concentrations at postsynaptic

membrane

Classified as selective serotonin reuptake inhibitors

(SSRIs)

Other SSRIs:

– Celexa, Luvox, Paxil, and Zoloft

Brain Chemistry

Parkinson Disease

Inadequate dopamine production causes motor

problems

Dopamine

Secretion stimulated by amphetamines, or “speed”

Large doses can produce symptoms resembling

schizophrenia

Important in nuclei that control intentional movements

Important in other centers of diencephalon and cerebrum

Nervous System Integration

Neural Tissue

Extremely delicate

Extracellular environment must maintain

homeostatic limits

If regulatory mechanisms break down,

neurological disorders appear


Figure 16–16 Functional Relationships between the Nervous System and Other Systems.





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Putting it all together-Neural integration Muse lecture #16 Ch 15-16.

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