a&p mod 12 - somatic nervous system

sensory (afferent) division

carries sensory information from receptors to CNS

motor (efferent) division

carries motor commands from CNS to effector organs

somatic nervous system

controls voluntary movements (skeletal muscle)

autonomic nervous system

controls involuntary movements

sensory neurons

brings sensations into CNS

afferent fibers

sensory axon

interneurons

relay signals from sensory to motor neurons; responsible for higher functions

motor neurons

transport signal to effector

efferent fibers

motor axons

sensory receptors

specialized cells/cell processes that alert CNS about conditions in/out of your body

interoceptors

monitor internal organs/systems; detect dissension, deep pressure, pain

proprioceptors

monitor position/movement of skeletal muscles/joints

exteroceptors

monitor external environment; special senses

ganglion

collection of neuron cell bodies in PNS

somatic sensory neurons

external monitor and body position (propioceptors & exteroreceptors)

visceral (autonomic) sensory neurons

internal monitor (interceptors)

somatic motor neurons

transport signal to skeletal muscles

visceral (autonomic) motor neurons

transport signal to cardiac muscle, smooth muscle, glands, adipose tissue, etc

general senses

senses without a specialized organ

special senses

senses that have receptors located within specialized organs

sensation

signal carried by a sensory pathway; requires receptor activation and sensory neuron activation

perception

conscious awareness of a sensation; requires sensory signal reaches cortex, signal is processes, and signal is sent to be made "aware" of

nociceptors

pain receptors with free nerve endings; do not adapt quickly

thermoreceptors

temperature receptors; free nerve endings in dermis, skeletal muscles, liver, hypothalamus

chemoreceptors

respond to chemical concentrations; substances dissolved in body fluids

mechanoreceptors

respond to mechanical distortion of their plasma membranes

propioceptors

position of joints/muscles

baroreceptors

detects pressure changes

tactile receptors

touch (shape/texture), pressure, and vibration

receptive field

area monitored by single receptor cell

large receptor field =

decreased detail

small receptor field =

increased detail

tonic receptors

slow-adapting, always active; AP frequency reflects level of stimulation; increased stimulus = increases AP frequency

phasic receptors

fast-adapting; normally inactive; become active for a short time when a change occurs in what they are monitoring

adaption

reduction in sensitivity with constant stimulus

peripheral adaptation

receptor threshold increases; activity declines

central adaptation

nuclei along a sensory pathway are inhibited; signal lessened

somatotopy

functional map of the body in the brain

homunculus

somatotope showing the relative size of somatosensory or motor cortex devoted to any specific body area

3-neuron pathway

neuron 1: receptor -> spinal cord/brainstem

neuron 2: spinal cord/brainstem -> thalamus

neuron 3: thalamus -> cerebral cortex

lateralization of 3 neuron pathway spinal nerves

right side receptor -> left cortex

left side receptor -> right cortex

lateralization of 3 neuron pathway cranial nerves

right side receptor -> right cortex

left side receptor -> left cortex

2-neuron pathway

neuron 1: receptor -> spinal cord

neuron 2: spinal cord -> cerebellum

lateralization of 2-neuron pathway

both sides go to both sides:

right -> L&R cerebellar hemispheres

left -> R&L cerebellar hemispheres

upper motor neuron

motor cortex -> midbrain/spinal cord

somatic motor pathways

motor responses (effects) must be sent to a skeletal muscle (effector)

lower motor neuron

midbrain/spinal cord -> effector

somatic motor control process

frontal lobe, premotor cortex, basal nuclei/cerebellum, precentral gyrus, effectors

referred pain

sensation of pain in a a part of the body other than its actual source; strong visceral pain sensations arriving at a spinal cord segment can stimulate interneurons in spinothalamic pathway

parkinson's disease

substantia nigra neurons degenerate, basal ganglia control is spotty; movements become shaky

rabies

virus carried by axons back into CNS through retrograde flow; affects various mental processes, notable invasion of salivary glands

amyotrophic lateral sclerosis (ALS)

progressive degenerative disorder affecting motor neurons in spinal cord, brainstem, cerebrum; destroys upper/lower motor neurons, associated skeletal muscles atrophy; sporadic and inherited

alzheimer's disease (AD)

Progressive disorder causing loss of higher-order cerebral functions; intracellular and extracellular abnormalities in hippocampus (affects memory processing)

multiple sclerosis (MS)

CNS disease characterized by autoimmune-driven demyelination of axons of optic nerve, brain, spinal cord; Common signs/symptoms include impairment of vision, speech, balance, general motor coordination