human phys test 2

CNS role

receives sensory inputs, coordinates response of the organs and functions of the body

CNS includes

spinal cord, brainstem, cerebellum and cerebrum

ventricles and central canal

filled with cerebral spinal fluid

cerebral cortex

“bark of the brain”, where cerebral neurons are located

gray matter

cell bodies of neurons

white matter

axon fibers of neurons (the wires)co

corpus callosum

the giant fiber bridge that connects the two hemispheres of the cerebrum

gyrus

the bulging part of a wrinkle on the cortex

sulcus

the valley of the fold (in between the wrinkles)

more connections in cortex lead to

greater surface area and more wrinkly brain, axons try to minimize difference between connected neurons

inputs to the CNS

cranial sensory nerve, sensory ganglion

outputs from the CNS

Cranial motor nerves, autonomic nerve, autonomic ganglion, motor neurons, motor nerve

cranial nerves

sensory and motor nerves that come straight to and from the brain

frontal lobe

voluntary motor control of skeletal muscles; personality; higher intellectual processes (e.g., concentration, planning, and decision making); verbal communication

Parietal

Somesthetic interpretation (e.g., cutaneous and muscular sensations); understanding speech and formulating words to express thoughts and emotions; interpretation of textures and shapes

Temporal

interpretation of auditory sensations; storage (memory) of auditory and visual experiences

occipital

integration of movements in the eye; correlation of visual images with previous visual experiences and other sensory stimuli; conscious perception of vision

insula

memory; sensory (principally pain) and visceral integration

somatosensory cortex

located behind the central sulcus, termination of sensory (touch) information coming from skin

motor cortex

located right in front of the central sulcus, cerebral neurons that initiate movement, sending axons directly and indirectly to spinal neurons

homonculus

topographic map of sensory input to the somatosensory cortex and motor output of motor cortex

• parts of the body with highest density of sensory receptors get a bigger share of the somatosensory cortex dedicated to processing

• parts of the body with the finest motor control (most muscles) get a bigger share of the motor cortex

brainstem

monitors internal chemical signals and controls autonomic function, carries out reflexive functions to respond to acute (immediate) changes in bodily function (like postural changes in blood pressure)

hypothalamus

uses neural and endocrine signals to monitor peripheral variables, controls long-term homeostasis by hormonal signals via the pituitary gland or by neural outputs through the brainstem

Autonomic system

involuntary with two step projection

1. spinal/brainstem pre-ganglionic neuron synapses onto post-ganglionic neuron

2. post-ganglionic neuron synapses onto target smooth muscle (in blood vessel, glands)

somatic motor system

voluntary, spinal motor neuron synapses onto target skeletal muscle

sympathetic nervous system

nerves from spinal cord run to chain ganglia or collateral ganglia and then to glands and smooth muscle

• mobilize energy, divert blood to muscle, prepare to flight or flee

parasympathetic nervous system

nerves from the brainstem and spinal cord run to glands and smooth muscle, prepare for digestion, energy storage, divert blood flow to gut (rest and digest)

What kind of muscle is striated

skeletal muscle, the actin and myosin are arranged in sarcomeres

what kind of muscle is not striated

smooth muscle, more actin than myosin, actin inserts into dense bodies and cell membrane

skeletal muscle contains

well-developed sarcoplasmic reticulum and transverse tubules, contains troponin in the thin filaments

smooth muscle contains

poorly developed sarcoplasmic reticulum; no transverse tubules, contains calmodulin, a protein that, when bound to Ca2+, activates the enzyme myosin light-chain kinase

Ca2+ movement in skeletal muscle

released into cytoplasm from sarcoplasmic reticulum

Ca2+ in smooth muscle

enters cytoplasm from extracellular fluid, sarcoplasmic reticulum, and perhaps mitochondria

Skeletal muscle and nerves

cannot contract without nerve stimulation; denervation results in muscle atrophy

smooth muscle and nerves

maintains tone in the absence of nerve stimulation; visceral smooth muscle produces pacemaker potentials; denervation results in hypersensitivity to stimulation

skeletal muscle activation

muscle fibers are stimulated independently; no gap junctions

smooth muscle activation

gap junctions are typically present

where are skeletal muscles found

attached to tendons and bones; contracts to move skeleton, the receptors are found at the neuromuscular junction

where are smooth muscles found

wrapped around blood vessels, GI tract, glands; contracts to constrict vessels or squeeze glands, neurotransmitter receptors all over cell surface

types of filaments in muscle

Actin and myosin diagram

what kind of contractions does smooth muscle have

spontaneous contractions

Smooth Muscle activation cascade

• depolarization - voltage-gated Ca2+ channels open in plasma membrane

• Ca2+ and calmodulin go into the calmodulin-Ca2+ complex

• phosphorylation of cross bridges leads to contraction

• dephosphorylation of cross bridges leads to relaxation

sympathetic chain of paravertebral ganglia

• connected to the spinal roots by white ramus (preganglionic going into ganglion) and gray ramus (postganglionic leaving out of ganglion)

  • convergence of inputs leads to mass activation of postganglionic neurons

  • postganglionic fibers join in spinal nerves, innervate blood vessels et al. in skeletal muscles and skin

splanchnic nerves

• sympathetic preganglionic fibers below the diaphragm project to collateral ganglia

• postganglionic fibers from collateral ganglia innervate digestive, urinary, reproductive organs

medulla of adrenal gland

• modified sympathetic ganglion

• postganglionic fibers stimulate medullary cells to secrete epinephrine and norepinephrine into the blood

preganglionic nerves

release acetylcholine (ACh) to stimulate nicotonic receptors on postganglionic cells

postganglionic cells

release norepinephrine (NE) to stimulate or inhibit target tissues via adrenergic receptors

sympathetic fibers to sweat glands

use ACh

Acetylcholine → cholinergic receptors

• nicotinic (ligand gated Na+ channels)

• muscarinic (g-protein-coupled receptors)

Norepinephrine → adrenergic receptors

• epinephrine from adrenal gland

  • alpha-adrenergic receptors (G-protein-coupled receptors)

  • beta-adrenergic receptors (G-protein-coupled receptors)

ACh

released by both sympathetic and parasympathetic preganglionic neurons, to stimulate nicotinic receptors on postganglionic cells

• nicotinic receptors are blocked by curare

Parasympathetic postganglionic neurons release ACh where

onto muscarinic receptors, which are blocked by atropine (belladona extract)

muscarinic receptors

G-protein-coupled receptors that have stimulatory or inhibitory effects on target organ, depending on the specific receptor subtype (M1-5)

sympathetic postganglionic neurons release NE where

onto adrenergic receptors

adrenergic receptors

a G-protein-coupled receptor that has stimulatory or inhibitory effects on target organ, depending on the receptor subtype

• adrenergic receptors are blocked by alpha or beta blockers

dual innervation

most target organs are innervated by sympathetic and parasympathetic fibers, the effects are normally antagonistic (but can be complementary or cooperative)

organs that receive only sympathetic innervation

adrenal medulla, skin (arrector pili and sweat glands) and most blood vessels

where are nicotinic ACh receptors found

post synaptic membrane of

• all autonomic ganglia

• all neurotransmitter junctions

• some CNS pathways

ligand-gated channels (ion channels are part of receptor)

muscarinic ACh receptors

• produces parasympathetic nerve effects in the heart, smooth muscles and glands

• g-protein-coupled receptors (receptors influence ion channels by means of G-proteins)

• hyperpolarization (k+ channels open → inhibition/slower heart rate), depolarization (K+ channels close → excitation/smooth muscles of the digestive tract contract)

Example of one NT with multiple effects

epinephrine (adrenalin) secreted from Adrenal gland and autonomic neurons during stress

pupil dilation

light via optic nerve (II) stimulates parasympathetic nerve (III) to constrict pupillary sphincter muscle (ACh muscarinic receptor), blocked by atropine → pupil dilation.

• sympathetic nerves stimulate the pupillary dilator muscle (NE beta-adrenergic receptors)

• cocaine → enhanced NE levels → enhanced dilation

Hidrosis (sweating)

sympathetic postganglionic neurons synapse onto sweat glands in the skin, they release ACh to stimulate sweating

hyperhydrosis

excessive sweating — treated with anticholinergics, botulin toxin (botox) that blocks ACh release, or sympathectomy (cutting sympathetic nerves)

horner’s syndrome

damage to sympathetic nerves on one side of the neck, unilateral (one-sided) constriction of pupil, anhydrosis (lack of sweat), flushing

• drooping eyelid (ptosis)

• constricted pupil

• reduced sweating on the affected facial side

organophosphates

insecticides that block cholinesterase enzyme → enhanced ACh neurotransmission at all synapses, treated with atropine to block effects of elevated ACh

cocaine

in dim light, increases nor epi levels, so pupil dilates

atropine

in bright light, blocks muscarinic ACh receptors, so blocks parasympathetic constriction, so pupil dilates

organophosphate pesticides

malathion and nerve gas (sarin) are AchE inhibitors, poisoning will present with symptoms of cholinergic activation

nicotinic ACh receptors

they are on ganglionic synapses, neuromuscular junction and parasympathetic target synapse

inhibition of AChE by organophosphates

causes increased ACh in cholinergic synapses, so bigger, longer response

stimulus modality

touch, pressure, vibration, chemicals, light

neural response

rate of firing proportional to stimulus strength, phasic vs tonic firing patterns

sensory receptor cells

different for each sensory modality

receptive fields

the range of stimulus (e.g. a particular sound frequency) or the area covered by the stimulus (e.g. a particular spot on the skin) that causes a sensory neuron to respond

central representation

how does the peripheral sensory input get mapped onto the cerebral cortex

central feature extraction

from the raw input of the peripheral sensory neurons, the cortex extracts more complex features, ultimately resulting in cognition)

mechanoreceptors

stimulated by mechanical force, deforms the cell membranes of sensory dendrites or deforms hair cells that activate sensory nerve endings

mechanoreceptor examples

cutaneous touch and pressure receptors; vestibular apparatus and cochlea

pain receptors

activated by tissue damage, damaged tissues release chemicals that excite sensory endings

pain receptor examples

cutaneous pain receptors

chemoreceptors

activated by dissolved chemicals, chemical interaction affects ionic permeability of sensory cells

photoreceptors

activated by light, photochemical reaction affects ionic permeability of receptor cells

chemoreceptor examples

smell and taste (exteroceptors), osmoreceptors and carotid body chemoreceptors (interoceptors)

photoreceptor examples

rods and cones in the retina of the eye

phasic receptor

fast-adapting

tonic receptor

slow-adapting

somatosensation

mechanoreceptors that respond to touch/pressure on the surface of the body, sensory nerve responds proportional to pressure

Meissner corpuscles and Merkel discs

cutaneous light touch with high resolution, rapidly adapting (phasic receptors)

Pacinian corpuscles and Ruffini endings

deep receptors responding to stronger force with less activity, slowly adapting (tonic response)

free nerve endings

respond to temperature and painful stimuli

receptive fields

map to specific area on the body, density of receptive fields varies across the body (lips, fingers have highest density so most sensitive)

two touch discrimination

maps out receptive field density

small point

causes intense pressure over small area

large point

spreads pressure over wider area

free nerve endings structure

unmyelinated dendrites of sensory neurons, light touch; hot; cold; nociception (pain)

free nerve endings location

around hair follicles

merkel’s disc structure

expanded dendritic endings, sustained touch and pressure, base of epidermis

ruffini corpuscles (endings)

enlarged dendritic endings with open, elongated capsule, sustained pressure, deep in dermis

messiner’s corpuscles

dendrites encapsulated in connective tissue, changes in texture, slow vibration, upper dermis