Purpose of nervous system maintaining homeostasis using rapid nerve

impulses (action potentials) movement memories behavior

functions: Sensory function: afferent (sensory) neurons

detect internal and external stimuli and carry message to brain

Integrative function: processes sensory information

Motor function: produces a motor response after processing sensory information. Efferent (motor) neurons carry information to effectors (muscles and glands)

Organization of nervous system 2 main subdivisions: central (CNS) – brain

and spinal cord - and peripheral (PNS) – nervous tissue outside CNS.

Further subdivisions PNS: somatic (voluntary) nervous system and

autonomic (involuntary) nervous system Somatic: sensory neurons (to the brain) and

motor neurons (from the brain – cranial and spinal nerves - to skeletal muscles)

Autonomic: sensory neurons (to brain from visceral organs) and motor neurons (from brain to smooth muscle, cardiac muscle, and glands)

Motor part of ANS: sympathetic (“fight or flight”) and parasympathetic (“rest and digest”)

Peripheral Nervous System

A look at its two branches: somatic and autonomic

Somatic nervous system Controls skeletal muscles

Cranial nerves Spinal nerves/plexuses

Cranial nerves 12 pairs

Assigned roman numeral (indicate order from anterior to posterior) and a name (designate nerve’s distribution or function)

Ex: Olfactory (I) nerve

and

Optic (II) nerve

Spinal nerves/plexuses - 31 pairs form complex

network of nerves serving the limbs = plexus

Important plexuses: cervical, brachial, lumbar and sacral

Cervical plexus

Brachial plexus Important nerves:

Axillary Median Ulnar Radial

Lumbar plexus Originates L1-L4

Important nerves: Femoral Obdurator

Sacral plexus Originates L4-L5;S1-

S4

Important nerve: sciatic

ASSIGNMENT CREATE A CHART (TREE) THAT

CLASSIFIES ALL THE DIVISIONS OF THE NERVOUS SYSTEM

Neuron physiology

Neuron physiology Background:

inactive neuron – polarized (more + in extracellular space).

Extracellular: mainly Na+

Intracellular: mainly K+

Inactive until excited by stimulus (threshold = generator potentialgenerator potential) EX. 1: light, sound, touch EX. 2: neurotransmitters

stimulus causes: Open Na+ gates Diffusion of Na+ Charge (polarity) changes – depolarization. A

situation called a graded potential (inside more positive)

Neuron transmits an action potential (nerve impulse) – a long distance signal.

Na+ gates close; K+ diffuses out: Returns cells to beginning electrical conditions (repolarization)

Activation of sodium-potassium pump (uses ATP)

Propagation of action potential in neurons with myelin sheaths:

Impulses jump from node to node

Myelin sheath: covering on some neurons that increases the speed of nerve impulse conductions

Neuron speed related to its anatomy Myelin sheath: covering on some neurons

that increases the speed of nerve impulse conductions Amount increases from birth to maturity. (a baby

is not as coordinated as adult)

Nodes of Ranvier: gaps in myelin sheath

How neurons transmit a message Neurotransmitters Extracellular space: Synaptic cleft

(synapse) Repeat in subsequent neurons

Reflexes Rapid, predictable, and involuntary

responses Occur over neural pathways called reflex

arcs Types: somatic (stimulate sk. muscles) and

autonomic (smooth muscles, heart, glands) Indicate health of nervous system

Parts: reflex arc1. Sensory receptor –

reacts to stimulus

2. Sensory neurons:

3. Integration center: synapse between sensory/motor neurons

4. Motor neurons:

5. Effector organ – muscle/gland that responds (the reflex)

Neurotransmitters Acetylcholine: excitatory at NMJ Dopamine: active in emotional responses,

addictive behaviors, pleasurable experiences, contraction of some sk. muscle

Serotonin: control of mood, appetite, and the induction of sleep.

Nitric oxide: causes vasodilation. Lowers bp and causes erection in penis. (viagra enhances the effect of NO)

Endorphins: natural painkillers, feelings of euphoria

Modifying the effects of neurotransmitters

Stimulated or inhibited by drugs. EX: Parkinson patients take a drug to boost

dopamine production in brain Botulinum toxin blocks release of acetylcholine

Neurotransmitter receptors can be activated or blocked. EX: Isuprel- drug to treat asthma attack – it

binds to receptor and mimics/enhances natural neurotransmitter effect

Neurotransmitter removal can be stimulated or inhibited. EX: cocaine blocks dopamine reuptake

Parkinson's disease: degeneration of neurons that release dopamine causing involuntary skeletal muscle contractions