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

Background: inactive neuron – polarized (more + in extracellular space). Extracellular: mainly Na + Intracellular: mainly K +

generator potential Inactive until excited by stimulus (threshold = generator 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 arc 1. 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