Chapter 12 Flashcards
Central Nervous system
brain and spinal cord
Peripheral nervous system
nerves and ganglia
Sensory nervous system
Afferent = arrives to CNS. detects stimuli and transmits info from receptors to cns. Has somatic and visceral sensory. somatic is consciously perceived by receptors and visceral is not consciously perceived
Motor Nervous system
initiates and transmits info from cns to effectors. Somatic is motor output voluntarily controlled and autonomic is not.
Neuron
sends and receives signals; processes info.
synapse
where neurons “connect” to another neuron or effector. Chemical or electrical
chemical synapse
more common and precise and selective. use neurotransmitters and are composed of a presynaptic neuron (produces signal) and postsynaptic neuron (signal receiver). knob almost touches; gap called synaptic cleft.
Neurotransmitters
chemicals in the synaptic knob. Are released through vesicles and diffuse across cleft binding to another neuron.
synaptic delay
time between neurotransmitter release and binding
electrical synapse
rare: neurons are physically toughing and have gap junctions
pumps
type of transport protein that move substances against concentration gradient and require energy.
channels
move substances down concentration gradient
leak channels
channels that are open for continuous diffusion
chemically gated channels
normally closed; open in response to binding of a neurotransmitter. Allow a specific type of ion to diffuse when open
voltage gated channels
normally closed, open in response to changes in electrical charge across membrane.
3 stages of voltage-gated na channels
have an activation gate and inactivation gate.
stage 1: resting state. inactivation gate open, activation closed. entry of Na is prevented
stage 2: activation state. inactivation open, activation open; na moves through
stage 3: inactivation state: activation and inactivation closed; Na entry is prevented.
stage 4: resting stage reestablished
distribution of leak channels
K and Na leak channels are present throughout entire neuron. more K present; easier to go through. Helps maintain resting membrane potential
receptive segment
includes dendrites and cell body. Chemically gated channels are here, but few voltage-gated.
initial segment
composed of axon hillock (top of axon). contains voltage gated Na and K channels
conductive segment
length of axon and its branches. contains voltage gated Na and K channels
Transmissive segment
includes synaptic knobs. contains voltage gated Ca channels and pumps
events of an action potential (6)
- unstimulated axon has resting potential of -70mv
- graded potentials reach axon hillock and are added together
- depolarization occurs when the threshold of -55mv is reached; voltage gated Na channels open until membrane reaches +30mv
- repolarization occurs due to closure of Na channels and opening of K channels to move potassium out of cell. Happens until -90mv
- hyperpolarization occurs due to K channels being open to long. They reach -90 instead of -70mv.
- Voltage gated K is closed and plasma membrane is returned to normal by Na/K pumps
4 steps of releasing a neurotransmitter
- action potential reaches synaptic knob
- voltage gated Ca channels open and Ca binds to proteins of synaptic vesicles containing neurotransmitters
- Synaptic vesicles merge with plasma membrane and neurotransmitter is released by exocytosis.
- Neurotransmitter crosses synaptic cleft and attaches to receptors on a muscle, neuron, or gland.
Somatic nervous system
part of the motor output. voluntary part of the nervous system in control of skeletal muscles
Autonomic nervous system
part of motor output for involuntary muscles
sympathetic nervous system
part of autonomic motor output that initiates the fight or flight response.
parasympathetic nervous system
part of autonomic system that conserves energy.
what causes voltage?
positively charged ions
resting membrane potential
-70mv
polarized neuron
positive on outside, negative on inside
sodium potassium pump
for every 2 K it pumps in, it pumps 3 Na out
graded potential
a potential that does not reach -55 mv and does not stimulate voltage gated channels
conduction velocity
how fast an action potential travels. myelin sheaths conduct action potential faster.
saltatory conduction
when action potential jumps between myelin sheaths.
excitatory neurotransmitter
depolarizes the neuron making the inside more positive and more likely to send a signal to other neurons.
inhibitory neurotransmitter
hyperpolarizes the neuron by making it more negative on the inside (either takes K+ out of cell by opening chemically gated K channels or opens Cl- channels to bring Cl- into cell); prohibits signal from moving.
