Nervous System (Ch 12)

basic division of nervous system

central nervous system and peripheral nervous system

Central nervous system (CNS)

the brain and spinal cord; command center

Peripheral nervous system (PNS)

nerves extending from brain and spinal cord; spinal nerves, cranial nerves, ganglia

ganglia

clusters of neuronal cell bodies in the PNS

sensory (afferent)

• signals picked up by sensor receptors, input; PNS → CNS

• Somatic sensory, visceral sensory

nerve vs neuron

• nerve = bundle of axons

• neuron = a single nerve cell body

motor (efferent)

• signals are carried away from the CNS; output

• Somatic motor, Visceral motor

sensory and motor divided into?

• Somatic body region— Skeletal muscle, bones, integument

• Visceral body region— Visceral organs, heart, glands

somatic sensory

• General somatic senses

• Proprioceptive senses

• Special somatic senses

General somatic senses

receptors spread throughout outer tube of body (touch, pain, vibration, pressure, temperature)

Proprioceptive senses

detect stretch in tendons and muscle; position and movement of body in space

Special somatic senses

Hearing, balance, vision

General visceral senses

widely felt in digestive and urinary tracts, and reproductive organs (stretch, pain, nausea, hunger)

Special visceral senses

taste and smell

Somatic motor

signals contraction of skeletal muscles; voluntary nervous system

Visceral motor

regulates the contraction of smooth and cardiac muscle; “involuntary nervous system”

neurons

cells that conduct electrical impulses; nerve impulse (action potential)

Special characteristics of neurons

• Longevity

• Do not divide

• High metabolic rate

anatomy of neuron’s cell body

• organelles plus other structures

• located within the CNS

• ganglia

dendrites

transmit electrical signals toward the cell body

Axons

Transmits impulses away from the cell body

synapses

Site at the end of an axon terminal

Presynaptic neuron

Conducts signal toward a synapse

Postsynaptic neuron

Transmits electrical activity away from a synapse

Sensory neurons

Transmit impulses toward the CNS

Motor (efferent) neurons

Carry impulses away from the CNS

Interneurons

lie between motor and sensory neurons in the CNS

Neuroglia in the CNS

• Astrocytes

• Microglia

• Ependymal cells

• Oligodendrocyte

Astrocytes

most abundant glial cell type

• regulate neurotransmitter level

• produce molecules necessary for neuronal growth

Microglia

the macrophages of the CNS; eat at any bacteria

Ependymal cells

produce cerebral spinal fluid (CSF)

Oligodendrocytes

Produce myelin sheaths in the CNS

Neuroglia in the PNS

• satellite cells

• schwann cells

Satellite cells

surround neuron cell bodies within ganglia

Schwann cells

surround axons in the PNS; form myelin sheath in the PNS