The Nervous System

central nervous system functions

receives sensory stimuli from PNS

processes and interprets the stimuli at various parts of the brain or spinal cord

sends motor signals to the PNS

lobes of the brain

frontal lobe

parietal lobe

occipital lobe

temporal lobe

other important parts of the brain

cerebellum

brain stem

spinal cord

peripheral nervous system functions

communicator between our body and the CNS

body to the CNS via sensory receptors and sensory (afferent) neurons

CNS to the body via motor (efferent) neurons and effectors

how does the sensory division do its job

sensory receptors send stimuli information to the CNS via sensory (afferent) neurons

how does the motor division do its job

receives signals from the CNS via motor neurons which target muscles and glands (effectors)

sensory (afferent) division of the PNS

allows us to interpret our external environment and maintain our internal environment through transduction

transduction

conversion of a chemical/physical/light signal to an electrical signal so it can reach the CNS

structural types of sensory receptors

receptors with free nerve endings

receptors with encapsulated nerve endings

specialized receptor cells (like rods and cones)

receptors with free nerve endings

nerve endings (dendrites) are exposed, allowing them to receive all types of information

receptors with encapsulated nerve endings

nerve endings (dendrites) are encapsulated, making them limited in the information they can receive, but they receive it more sensitively/accurately

functional types of sensory receptors

chemoreceptors

mechanoreceptors

nociceptors

osmoreceptors

thermoreceptors

photoreceptors

chemoreceptors

chemical stimuli

located in lungs, blood, tongue, nasal cavity

mechanoreceptors

physical stimuli including pressure, vibration, sound, balance, stretch

located in skin, muscles, inner ear

nociceptors

pain or tissue damage stimuli

located in skin, muscles, visceral organs

osmoreceptors

solute concentration stimuli

located in hypothalamus and kidneys

thermoreceptors

temperature stimuli

located in skin and hypothalamus

photoreceptors

light stimuli

located in eyes

what are the 4 pathways

sensory (afferent) pathway

autonomic motor (efferent) neuron pathway

somatic voluntary motor (efferent) neuron pathway

somatic involuntary motor (efferent) neuron pathway (reflex circuit)

sensory (afferent) pathway

stimulus occurs at the dendrites

opens a gated-channel and ions flow into the cell, creating a graded potential

transduction converts the stimulus into the electrical signal (action potentials)

action potentials occur along the neuron and neurotransmitters are released at the end of each

eventually reaches the CNS where is it processed in a certain lobe

how can our CNS determine the strength of a stimulus

by the frequency of action potentials it receives from a sensory signaling pathway

more action potentials lead to more neurotransmitters released at the synapse

what changes the frequency of action potentials (weak stimulus)

a weaker stimulus triggers only a few receptors, causing a graded potential that only stays above the threshold for a short amount of time

just a couple action potentials are sent, so a small number of neurotransmitters are released

CNS receives a weaker signal and interprets that it is a weak stimulus

what changes the frequency of action potentials (strong stimulus)

a strong stimulus triggers many receptors, causing a graded potential that is above the threshold for a longer time

many action potentials are created, many neurotransmitters are released

CNS receives a strong signal and interprets that it is a strong stimulus

taste (gustation) pathway

stimulus: “tasty” molecules / tastants

sensory receptor name: taste cells (with taste hairs)

functional receptor: chemoreceptor - chemical into electrical

CNS processing location: frontal lobe (gustatory cortex)

smell (olfaction) pathway

stimulus: “smelly” molecules / odorants

sensory receptor name: olfactory receptors

functional receptor: chemoreceptors - chemical into electrical

CNS processing location: temporal lobe (olfactory cortex)

hearing (audition) pathway

stimulus: sound waves

sensory receptor name: hair cells in cochlea

functional receptor: mechanoreceptors - physical into electrical

CNS processing location: temporal lobe (auditory cortex)

vision pathway

stimulus: light waves

sensory receptor name: rods and cones

functional receptor: photoreceptors - light into electrical

CNS processing location: occipital lobe (visual cortex)

balance (equilibrium) pathway

stimulus: movement of endolymph in the vestibular apparatus

sensory receptor name: sensory hair cells

functional receptor: mechanoreceptors - physical into electrical

CNS processing location: cerebellum

touch (somatosensation) pathway

stimulus: pressure

sensory receptor name: Ruffini ending/Merkel’s disc/Pacinian corpuscle

functional receptor: mechanoreceptor - physical into electrical

CNS processing location: parietal lobe (somatosensory cortex)

motor (efferent) division of PNS

composed of motor (efferent) neurons that are coming from the CNS

CNS => PNS (muscles, glands, organs - effectors)

autonomic nervous system response type

completely involuntary

processes going on in the background - things like digestion, breathing, heartbeat, blood vessels, hormones that maintain homeostasis

autonomic nervous system effectors

organs/glands

cardiac muscle

smooth muscle

autonomic nervous system subdivisions

sympathetic and parasympathetic that together help regulate homeostasis

one is dominant over the other depending on our circumstances

sympathetic divison

fight or flight responses

parasympathetic division

rest and digest responses

ANS control centers

hypothalamus - main control

amygdala - emotional/stress responses

pons - respiratory center

medulla - cardiovascular center

somatic nervous system response type

mostly voluntary movements, but also reflexes (involuntary)

somatic nervous system effectors

skeletal muscles only

ganglia

meeting point of many neurons that allows for a coordinated signal on specific organs/muscles or groups of them

preganglionic neurons communicate with postganglionic neurons

autonomic motor (efferent) neuron pathway

motor neuron from CNS to ganglion (preganglionic) —> synapse in ganglion —> motor neuron from ganglion to target effector (organ, smooth or cardiac muscle)

sympathetic vs parasympathetic responses on the body

they have opposite effects on the same effectors

ex: sympathetic constricts blood vessels while parasympathetic dilates them; sympathetic releases stress hormones while parasympathetic inhibits them

nerve

many bunches of neurons grouped together + connective tissue + blood

differences in sympathetic vs parasympathetic signaling pathways

length of pre- and postganglionic neurons

• sympathetic: lengths are roughly even

• parasympathetic: preganglionic much longer than post

neurotransmitters released

• sympathetic: Acetylcholine from preganglionic, norepinephrine from postganglionic

• parasympathetic: Acetylcholine from both pre-and postganglionic neurons

preganglionic neuron

cell body located in CNS

targets a postganglionic neuron

postganglionic neuron

cell body in PNS/ganglia

targets an effector

autonomic varicosities

multiple neurotransmitter release points along the axon, allowing for the widespread distribution of neurotransmitters across the target effector

2 ways that the ANS achieves a coordinated response

presence of ganglia (meeting point for neurons)

varicosities

voluntary movements of SNS

involve conscious control

originate in motor cortex of frontal lobe

targets skeletal muscles only

involuntary movements of the SNS

reflexes - responses to external stimuli that are unconscious

usually only involves the spinal cord or brainstem

faster than voluntary movements

a circuit because stimulus PNS —> CNS —> skeletal muscles PNS

somatic voluntary motor (efferent) neuron pathway

disynaptic

motor cortex of frontal lobe —> upper motor neuron (entirely in CNS, brain to spinal cord) —> lower motor neuron (start in CNS spine, ends at site of movement PNS) —> effector

somatic involuntary motor (efferent) neuron pathway (reflex circuit)

stimulus at the sensory receptor (PNS) —> sensory neuron signal sent to the spine —> control center in the spine (sometimes an interneuron) (CNS) —> lower motor neuron to a skeletal muscle at area of stimulus (PNS) —> skeletal muscle reflex

sensory pathway # of neurons

unspecified because it varies

autonomic motor and somatic voluntary motor pathway # of neurons

2 motor neurons

somatic involuntary motor pathway # of neurons

1 sensory, 1 motor (and sometimes 1 interneuron)