Nervous System

Allied Health IHendersonville High School

Organization of Nervous System

The Neuron

6 questions about the Neuron1. What is it?2. Where is it?3. What does it do?4. What are the different kinds of neurons?5. What does a neuron look like? 6. What are the functions of the different parts

of a neuron?

The Neuron1. What is it?– Nerve Cell that is the building block of the nervous

system

2. Where is it?– Throughout the body

3. What does it do?– Transmits information in both electrical and

chemical forms throughout the body

4. What are the different kinds of neurons– Sensory, Motor, Interneurons

The Neuron

5. What does a neuron look like?

The Neuron8 parts of the neuron

6. What are the functions of the different parts?– Axon: Sending arm– Dendrite: Receiving fingers– Soma: Cell body not involved in transmission– Myelin Sheath: fatty insulatory– Schwann Cell: forms myelin sheath– Node of Ranvier: gaps in sheath to renew action

potential– Synapse: gap separating neurons– Neurotransmitter: chemicals that allow message to

“jump” across synapse

A Nerve

1. What is it?2. Where is it?3. What does it do?4. How is a nerve constructed? 5. What does a nerve look like?6. What are the different kinds of nerves?7. How does a nerve communicate with the

brain?

1. What is it?– cordlike structure of the body, comprising a

collection of nerve FIBERS

2. Where is it?– Throughout the body

3. What does it do?– Conveys impulses between a part of the central

NERVOUS SYSTEM and some other body region.

A Nerve

4. How is a nerve constructed? – Like a muscle:– an outer covering: the

epineurium. – Nerve fibers organize into

bundles: fascicles– Each fascicle surrounded by

the perineurium– Between individual nerve

fibers is an inner layer of endoneurium.

More about Nerves

AND…• What is a glial cell?

(neuroglia)• What is the difference

between a stimulus, an impulse, irritability and conductivity?

A Nerve5. What does a nerve look like?

A Nerve6. What are the different kinds of nerves?– Sensory, Motor, Autonomic– (afferent, efferent)

7. How does a nerve communicate with the brain?– plexus: interconnection of fibers which form new combinations – spinal cord tracts (exception: Cranial Nerves)

• Sensory-somatic: conscious awareness of the external environment and all our motor

• Autonomic: involuntary communication between brain and internal organs

Crossing Over of the Spinal Tracts• Impulses reaching the spinal cord from the left side of the body

eventually pass over to tracts running up to the right side of the brain and vice versa

Regeneration

• Regeneration of Nerve Fibers (cut or compressed axons)– Separated ends seal off and swell – Axon and myelin sheath (of injured site) disintegrates – Schwann cells and macrophages migrate to site to

phagocytize debris – Neurilemma remains intact and schwann cells

proliferate – Axon "sprouts", guided by schwann cells, gap to

original contact

Divisions of the Nervous System

Peripheral Nervous System

1. What is the peripheral nervous system?2. What does it do?3. Where are the nerves of the peripheral

nervous system?4. How do the nerves of the peripheral nervous

system communicate with the brain?5. What are the divisions of the peripheral

nervous system?

Peripheral Nervous System1. What is the peripheral nervous system?– One of the 2 divisions of the Nervous system• Central (brain and spinal cord) and Peripheral

2. What does it do?– connects the central nervous system (CNS) to the

limbs and organs.

Peripheral Nervous System

3. Where are the nerves of the peripheral nervous system?– Cranial: directly from brain to head and neck• 12 pairs• Either sensory, motor or mixed

– Spinal Nerves: from spinal cord and extend throughout the body in dermatomes, pass out between the vertebrae• 31 pairs

Cranial Nerves– I. Olfactory– II. Optic– III. Oculomotor– IV. Trochlear– V. Trigeminal– VI. Abducens– VII. Facial– VIII. Vestibulocochlear– IX. Glossopharyngeal– X. Vagus– XI. Accessory– XII. Hypoglossal

Peripheral Nervous System

4. How do the nerves of the peripheral nervous system communicate with the brain?– Dermatomes: somatic or musculocutaneous areas

served by fibers from specific spinal nerves– spinal cord tracts (exception: Cranial Nerves)• white matter of the spinal cord contains tracts which travel up

and down the cord– White matter: bundles of axons each coated with a sheath of myelin

5. What are the divisions of the peripheral nervous system?– Sensory-somatic (sensory and motor)– Autonomic

Autonomic Nervous System

1. What is the Autonomic Nervous System?2. What does it do?3. What are the divisions of the Autonomic

Nervous System?4. What do each of the divisions control?

Autonomic Nervous System

1. What is the Autonomic Nervous System?– sensory neurons and motor neurons that run

between the central nervous system and various internal organs

2. What does it do?– Monitors conditions in the internal environment

and brings about appropriate changes in them

3. What are the divisions of the Autonomic Nervous System?– Sympathetic, Parasympathetic and Enteric

Autonomic Nervous System• What do each of the divisions control?– Sympathetic: prepares the body for emergencies:

for "fight or flight" (and, perhaps, enhances the memory of the event that triggered the response)• prepares the body for violent activity

– Parasympathetic: returns the body functions to normal after they have been altered by sympathetic stimulation• reverses these changes when the danger is over.

– Enteric nervous system: meshwork of nerve fibers that innervate the viscera (gastrointestinal tract, pancreas, and gall bladder

Autonomic Nervous System

• Sympathetic (Adrenalin)– stimulates heartbeat – raises blood pressure – dilates the pupils – dilates the trachea and bronchi – stimulates glycogenolysis — the conversion of liver

glycogen into glucose – shunts blood away from the skin and viscera to the skeletal

muscles, brain, and heart – inhibits peristalsis in the gastrointestinal (GI) tract – Inhibits contraction of the bladder and rectum

Autonomic Nervous System

• Parasympathetic– slowing down of the heartbeat (as Loewi

demonstrated) – lowering of blood pressure – constriction of the pupils – increased blood flow to the skin and viscera – peristalsis of the GI tract

Reflexes1. What is a reflex?– direct connection between stimulus and response, does not

require conscious thought, a reflex is a quick involuntary action. 2. Where does a reflex come from?– spine

3. How does a reflex occur– the stimulus occurs– sensory neurons sense the stimulus– sends a message to your spinal cord (it doesn't reach the brain

right then)– spinal cord sends a message to motor neurons– reflex occurs– While this is happening, message goes on to brain (which is why

you feel the pain slightly after the event)

Reflex

• Reflex and Reflex Arc– Reflex = rapid, predictable motor response to a stimulus– Five components to reflex arc:

• Receptor (site of stimulus) • Sensory neuron (transmits afferent impulses to CNS) • Integration Center:

– Monosynaptic reflex (single motor or sensory neuron) – Polysynaptic reflex (multiple interneurons)

• Motor neuron (conducts efferent impulses) • Effector (muscle or gland

Central Nervous System

1. What are the components of the central nervous system?

2. What are the functions of each structure in the CNS?

3. What is the difference between gray matter and white matter?

4. What are the names of the protective linings in the CNS?

5. What is the name of the fluid surrounding the structures in the CNS?

Nervous System

CNS

1. What are the components of the central nervous system?– Brain• Cranial Nerves

– Spinal Cord

CNS2. What are the functions of each structure in the CNS?– Spinal Cord

• conducts sensory information from the peripheral nervous system (both somatic and autonomic) to the brain

• conducts motor information from the brain to our various effectors – skeletal muscles – cardiac muscle – smooth muscle – glands

• serves as a minor reflex center

– Brain• receives sensory input from the spinal cord as well as from its own

nerves (e.g., cranial nerves)• devotes most of its volume and power to processing its various

sensory inputs and initiating appropriate — and coordinated — motor outputs

CNS

3. What is the difference between gray matter and white matter?– white matter = bundles of axons each coated with

a sheath of myelin – gray matter = masses of the cell bodies and

dendrites – In the spinal cord, the white matter is at the

surface, the gray matter inside. – In the brain, this pattern is reversed.

CNS

4. What are the names of the protective linings in the CNS?– The Meninges

• Both the spinal cord and brain are covered in three continuous sheets of connective tissue, the meninges– From outside in, these are:

» the dura mater — pressed against the bony surface of the interior of the vertebrae and the cranium• Subdural space

» the arachnoid • Subarachnoid space

» the pia mater

CNS

5. What is the name of the fluid surrounding the structures in the CNS?– CSF flows uninterrupted throughout the central

nervous system • through the central cerebrospinal canal of the spinal

cord and • through an interconnected system of four ventricles in

the brain