Nervous System

2 nervous systems

central nervous system (CNS) and peripheral nervous system (PNS)

central nervous system function

control brain and spinal cord

peripheral nervous system function

spinal and cranial nerves that transmit info to and from the brain and spinal cord

2 divisions of peripheral nervous system

sensory (afferent) division: transmits impulses to the CNS

motor (efferent) division: transmits impulses from the CNS to the effectors (organs, glands, and muscles)

2 branches of motor division

somatic nervous system: conscious, voluntary control of skeletal muscles

autonomic nervous system: unconscious, involuntary control of smooth muscle, cardiac muscle and glands;

2 branches of autonomic nervous system

sympathetic: “fight or flight” that controls exercise, excitement, emergency, and embarrassment

parasympathetic: “Rest and digest” keeps energy use low and controls digestion, defecation, diuresis, and some reproductive activities

somatic nervous system

single neuron transmits a nerve impulse from the spinal cord to the skeletal muscles. contains Ach.

Heavy Myelination

rapid transmission of nerve impulses

autonomic nervous system

control most of the same organs and glands (dual innervation), the effects of one division are opposite to other division (antagonism), this allows us to respond to changing conditions

parasympathetic nervous system

utilizes two neurons to transmit nerve impulses from spinal cord to effector: preganglionic (long - Ach) and postganglionic (short - Ach) neurons

sympathetic nervous system

utilizes two neurons to transmit nerve impulses from the spinal cord to effector (except adrenal medulla): preganglionic (short and branching - Ach) and postganglionic (long - epinephrine) neurons

spinal nerves

31 pairs. contain both sensory and motor neurons however:

dorsal root = only sensory neurons

ventral root = only motor neurons

cauda equina

collection of nerve roots at the end of the vertebral canal

neuron

individual nerve cell that can only transmit nerve impulses in one direction:

sensory: toward the CNS

motor: away from the CNS

interneurons: within the CNS

Nerve

bundle of neurons that are typically a mixture of sensory and motor neurons (rarely only sensory)

White matter

neurons are myelinated so the nerve impulses travel very rapidly

Gray matter

neurons are unmyelinated so nerve impulses transmission is slower; time for processing

gray matter of spinal cord

dorsal (posterior) horns: interneurons

ventral (anterior) horns: interneurons and somatic motor neurons

lateral horns: contain sympathetic nerve fibers

Sensory Receptors

1. mechanoreceptors = touch, pressure, stretch

2. thermoreceptors = temperature change

3. photoreceptors = light

4. chemoreceptors = chemicals in solution (smell & taste) or changes in the chemical make-up of the blood or other bodily fluids

5. nocirecptors = pain

dermatomal map

shows spinal nerves that innervate each dermatome (skin segment)

reflex

unlearned, involuntary, rapid, predictable response to a stimulus. spinal cord responds to sensory input and initiates motor output independent of the brain

reflex arc

sequence of events when the spinal cord responds independently

5 components to reflex arc

1. sensory receptor

2. sensory neuron

3. interneuron

4. motor neuron

5. effector