chapter 12 human anatomy and physiology

sensory

afferent: sensory cells to the brain CNS

the input region

motor

efferent

motor neurons that conducts impulses away from the CNS to glands and muscles

motor system 

divided into

somatic 

autonomic 

functions of nervous system

sensation (PNS → PNS): detect stimuli from external or internal sensors

integration (CNS): immediate context and experience (memories/association) 

response (from CNS to PNS): voluntary or involuntary; muscle or gland response 

autonomic

separated into

sympathetic: fight or flight

parasympathetic: promotes relaxation

neurons

composed of:

soma (cell body)

processes (dendrits/axon)

soma/cell body

has organelles

in CNS: collections of nueron cell bodies are called nuclei

in PNS: called ganglia

processes: 

branched dendrites: info in

axon: info out 

axon parts

hillock: region where axon leaves cell body

axon terminals

myelin sheath and nodes of Ranvier

groups of axons =

tracts in CNS

nerves in PNS

neurons are

excitable

possess a polarized membrane which allows them to conduct messages

longevity

high metabolic rate: need oxygen, glucose, and ADP

large

amitotic: lose ability to divide

nissl 

granular structures found in the cytoplasm of neurons that are composed or rough endoplasmic reticulum and ribosomes 

dendrites

relays chemical signals as well as electrical signals towards the cell body

axoplasmic transport

creating action potentials and transmitting nerve away from the cell bodyre

retrograde transport

transmission from the axon back to the cell body 

axolemma

plasma membrane of the axon

axoplasma

cytoplasm of an axon, which is different in composition than the cytoplasm of the neuronal cell body

axon hillock 

the trigger zone: action potentials must reach this point before they can be converted into action potentials 

telodendira

fine, terminal branches of an axon that form synapses with other neurons or target cells to transmit signals

myelin sheath

covers some axons

white, fatty protein lipids

protects and electrically insulates

conduct impulses rapidly

white vs grey matter

white: has myelin sheaths

grey matter - cell bodies and synapses s

synapse allow for cell-cell communication

synapses with another neuron

neuromuscular junctions

neuroglandular synapses

neuro classifications: polar

bipolar: two distinct processes (axon and dendrite); special sense organs like olfaction and vision

unipolar: one process that includes axon and dendrite; central side soma; mostly sensory neurons in PNS

multipolar: one axon and multiple dendrites; mostly interneurons in CNS and mostly motor neurons in PNS (most common neurons in the CNS)

CNS neuroglia

astrocytes: connect neurons to capillaries; guide growing neurons (star-shaped); bulb at end that connect with capillaries; blood brain barrier

microglia: immune functions; have many branches act as macrophages

ependymal: line cavities of the brain and spinal cord; produce and circulate use cillia cerebrospinal fluid

oligodendrocytes: produce multiple myelin sheath 

PNS neuroglia

Schwann cells: produce myelin around large nerve fibers; act as phagocytic cells and important in regeneration 

satellite cells: similar to astrocytes; control chemical environment 

process of myelination

myelinating glia wrap several layers of cell membrane around the cell membrane of an axon segment

a single Schwann cell (PNS) insulates a segment of a peripheral nerve 

oligodendrocyte (CNS): may provide insulation for a few separate axon segments 

Nodes of Ranvier

gaps in myelin sheath; action potentials will jump from node to node during conduction

sensory-motor response

sensory neurons, like in the skin → graded potential if strong enough can produce an action potential → axon of sensory neuron enters the spinal cord → another neuron in the grey matter → conducted to the thalmus on the way up to the rest of the brain → synapse to the next neurons → ends when it reaches the appropiate part of the cerebral cortex → motor command is initiated → motor neuron relays the action potential to another motor neuron in the gray matter → axon of the motor neuron branches out and connects to a muscle through neuromuscular junction to cause contraction

neurophysiology: ion channels 

proteins in the membrane control the flow of ions 

leak channels and gated channels 

move down an electrochemical gradient

gated channels

voltage: respond to change in polarization; concentrated at axon hillock

chemical (ligand): respond to neurotransmitters

mechanical: responds to physical change/deformation

ion channels process

resting potential (cell membrane is polarized) → depolarization and creation of a graded potential → action potential → propagation of this down the axon

ion channels 

passive/leaky: protein channels that are always open that allow certain ions to pass through these channels responsible for maintating the resting membrane potential 

active/gated: open and close due to various signals; chemically gated channels open when the appropriate neurotransmitter binds to receptor; important in depolarization and the creation of an action potential; located only on the dendrites and cell body of the neuron 

voltage-gated channels: open in response to changes of membrane potential; important in action potential and only in axon 

mechanical: only respond to physical changes or deformations caused by exposure to touch, pressure, or vibration 

location of channels

chemically gated ion channels: cell body

voltage gated Na+ and voltage-gated K+ channels: axon

voltage gated: Ca2+ channels: dendrites at the end of the axon

charges inside and outside the neuron

is negatively charged (-70 mV); has high concentration of K+

outside of the membrane is positively charged; highest concentration of Na+

integral proteins restrict ion flow: K+ leaks out and Na+ leaks in; Na+/K+ pump maintains this concentration

local changes in membrane potential can be 

depolarizing (-70 mV to -55mV) 

hyperpolarizing (-70 mV to -100 mV) 

graded potential is greatest at:

stimulation sites

larger stimulus = larger change

longer duration = longer lasting change but not larger change

graded potential: 

sodium channels are opening and potassium channels are closing 

graded vs action potential

graded potential have decrimental: signals decays as it gets farther and farther away from origin of the stimulus

can go in both potential, while action potentials can only go in one direction

action potentials

are widespread change in membrane potential that are driven by voltage-gated channels

are the summation of de- and hyperpolarization at axon hillock

threshold opens voltage gated Na+ channel

all-or-nothing principle

from -60 mV to +30 mV

saltatory conduction 

when the action potential jumps from one Nodes of Ranvier to antoher 

very rapid form of signaling in myelinated axons 

hyperpolarization can occur

because the K+ channels are slow to close

→ membrane potential can actually go below -70 mV

Na+/K+ pumps

pumps out 3 Na+ out and 2 K+ in → resting membrane potential of -70 mV

graded potentials 

can produce temporary changes in membrane potentials 

depends on the size of stimulus 

some can cause depolarizing or hyperpolarizing 

continuous conduction

occurs in unmyelinated axon

voltage-gaged Na+ and K+ channels regenrate the action potential at each point along the axon, so voltage does not decay

conduction is slow because movements of ions and the fates of channel proteins take time and must occur before voltage regeneration occurs

postsynaptic processing

= net effect from summation of all neurotransmitter effects

→ excitatory postsynaptic potential (EPSP) with graded depolarization

→ inhibitory postsynaptic potential (IPSP) with graded hyperpolarization

neurotransmitters: cholinergic 

acetylcholine: excitatory (skeletal muscle) 

neurotransmitters: biogenic amines

dopamine, norepinephrine, and epinephrine (feel good catechloamines)

serotonin: mood, sleep, appetite & anger (inhibitory)

histamine

neurotransmitters: amino acids

GABA (gamma-aminobutryic acid): inhibitory

glutamate: excitatory

neurotransmitters: peptide

endorphins and enkephalins: inhibitory 

glutamate:

important in memory and learning

GABA

opens chloride channels and have indirect effect on potassium

receptor types 

ionotropic 

metabotropic 

ionotropic receptor

= a channel that opens when the nuerotransmitter binds to it

metabotripic receptor (GPRC)

causes metabolic changes in the cells when the neurotransmitter binds to it

after binding → G protein hydrolyzes GRP and moves the effector protein → G protein contacts the effector protein a second messenger is generated e.g. cAMP → second messenger can then go to cause changes in the neuron, such as opening or closing ion channels, metabolic changes, and changes in gene transcription