Functional Organization of Nervous Tissue

Chapter 11

The Nervous System• Components:

– Brain, spinal cord, nerves, sensory receptors

• Responsible for…– Sensory perceptions, mental activities,

stimulating muscle movements, secretions of many glands

• Subdivisions:– Central Nervous System (CNS) – Peripheral Nervous System (PNS)

Central Nervous System• Consists of brain

and spinal cord

• The structural & functional center of the entire nervous system which integrates incoming pieces of information & initiates an outgoing response

Peripheral Nervous System

• All other nerves

• All pathways going toward and away from the CNS

Nervous System Organization

Concept Check• What are the two divisions of the nervous

system? What are their parts?– CNS: Brain & Spinal Cord– PNS: nerves

• What are the functions of the CNS?– Integrates incoming information & initiates an

outgoing response

• What is the function of the PNS?– Conducts action potentials to and away from the

CNS

• What are some functions of the Nervous system?– Sensory perceptions, mental activities,

stimulating muscle movement, secretions of many glands

Cells of Nervous System• Neurons or nerve

cells– Receive stimuli and

transmit action potentials

– Organization• Cell body or soma• Dendrites: input• Axons: output

• Neuroglia cells– Support and protect

neurons

Types of Neurons

• Functional Classification– Sensory or afferent: action potentials

toward CNS (receives stimuli; could be a special sense organ)

– Motor or efferent: action potentials away from CNS (attached to a muscle or gland)

– Interneurons or association neurons: within CNS from one neuron to another

Myelinated and Unmyelinated Axons

• Myelinated axons– Myelin protects and

insulates axons from one another

– Not continuous• Nodes of Ranvier• Impulse “jumps” from

node to node• Fast impulse

• Unmyelinated axons– Slower impulse

Electrical Signals

• Cells produce electrical signals called action potentials

• Transfer of information from one part of body to another

• Electrical properties result from ionic concentration differences across plasma membrane and permeability

Nerve Impulses• A wave of electrical fluctuation that

travels along the plasma membrane; due to changes in chemical concentrations.

----+----+--+--------+

++++-++++++-+++++- -----+----+-------+--+-------+--------

----+----+---+---------- ++++++++-++-++++-++

----+-----++-----------+-----+------+---

+++-++++++-++++-+

---+---+-----------+--+ ++++++-+++-++-+++++-++++++++

++++++-++-+++++++

--------+--++----------+---- +++++++-+++++++--++++++++-+++

Impulse

Resting Potential

“Polarized”

Action Potential

“Depolarized”

Resting Potential

“Repolarized”

Resting Membrane Potential• Characteristics

– Number of charged molecules and ions inside and outside cell nearly equal

– Concentration of K+ higher inside than outside cell- negative proteins in also, Na+ higher outside than inside

– At equilibrium there is very little movement of K+ or other ions across plasma membrane

Action Potentials• Series of permeability

changes when a local potential causes depolarization of membrane

• Phases– Depolarization

• More positive

– Repolarization• More negative

• All-or-none principle– Neuron will fire or it

won’t

The Synapse

• Junction between two cells

• Electrical message transferred across the synapse by chemicals called neurotransmitters

Concept Check• What are the main parts of a neuron?

– Axon, dendrites, myelin sheath, synapse

• What are the three types of neurons and what do they do?– Sensory (afferent)- action potential toward CNS ,

Motor (efferent)- action potential away from CNS, & Interneurons- within CNS from one neuron to another

• How does an impulse travel along an axon? What speeds it up?– Jumps from node to node; myelin

• How does a synapse work?– Neurotransmitters transfer message across synapse

Stimulus

• Any change in your environment.– Temp, sound, smell

• You may or may not respond to a specific stimulus

Reflex• A predictable response to a stimulus

which may or may not be conscious

– A reflex consists of either muscle contraction or glandular secretion

– Neurons involved in reflex• Afferent neuron- sensory• Interneuron• Efferent neuron- motor

Sensory Receptors• In order for a stimulus to be detected, it

must be strong enough to elicit an impulse– It must be at the threshold level- the

minimum stimulus to start an impulse

• The all-or-none response means that either a neuron will fire or it won’t, there is no partial impulse

• Sensation- the brain’s interpretation of what the stimulus is

Characteristics of Sensations

• Projection- brain refers a sensation to the point of stimulation

• Adaptation- loss of sensation even though the stimulus is still applied

• Afterimage- persistence of a sensation even though the stimulus is removed

• Referred pain- felt in the skin near or around the organ sending the impulse

• Phantom pain- sensation of pain in a limb that has been amputated

Classification of Receptors1. Mechanoreceptors- activated by

mechanical stimuli or deformation of the receptor

2. Chemoreceptor- changing of the chemical concentrations around the body

3. Thermoreceptors- detect hot and cold

4. Nociceptors- any stimuli that can cause tissue damage; sensation of pain

5. Photoreceptors- respond to light

Somatic Sensespain, temperature and touch

• These sensations can be felt throughout the body, yet they are distributed unevenly through the skin

• Exteroceptors- sense receptors located on body surfaces

• Proprioceptors- found in the muscles and joints

• Visceroceptors- found in internal organs

• Nociceptors- pain receptors; free nerve endings

Review

• Meissner’s corpuscles- touch

• Krause’s End Bulbs- touch

• Ruffini’s corpuscles- continuous touch

• Pacinian corpuscles- deep pressure

The Brain

• Parts/Functions• Left vs Right Brain Activity??• Dissection notes…pre-lab??