VM 602 Neuro

Peripheral Nervous System (PNS)

-conveys info to and from CNS

info from PNS toward CNS

afferent

info from CNS to PNS (away from CNS)

efferent

Central Nervous System (CNS)

-integrates sensory info

-generates output

anatomical classification of PNS

cranial and spinal nerves

anatomical classification of CNS

brain and spinal cord

aggregations of fibers in CNS

white matter

aggregations of cell bodies in the nervous system (ganglia, nucleus)

grey matter

bundle of nerve fibers which cross the midline/ connect hemispheres of the brain

commissure

bundle of nerve fibers in CNS

tract

bundle of nerve cell projections (axons) in PNS

nerve

group of neurons in a cluster- PNS

ganglion

group of neurons in a cluster- CNS

nucleus

_______ is made up of nerves and ganglia outside of the brain

PNS

CNS mesencephalon

midbrain

CNS metencephalon

pons

CNS myelencephalon

medulla

brainstem composed of

medulla, pons, midbrain

executive function part of brain

frontal pole

motor part of brain

frontal lobe

sensory part of brain

parietal lobe

visual part of brain

occipital lobe

auditory part of brain

temporal lobe

specialized epithelial cells that line the ventricles of the brain and spinal cord

ependyma

ependyma function

move CSF through ventricular system

spaces within brain and spinal cord where CSF flows

ventricular system

choroid plexus function

-secretes CSF

-significant role in blood-CSF barrier

-specialized ependymal cells

specialized neuron that detects change in external or internal environment and sends info about these changes to CNS

-from CNS to periphery

sensory neurons

neuron that controls contraction of muscle or secretion of a gland

-originate in CNS, project outside

motor neurons

neuron located entirely within the CNS

interneuron

neuron structure: 4 basic parts

1. dendrites

2. cell body (soma/ perikaryon)

3. axon

4. terminal boutons

dendrites

-emanate from cell body

-receive input

-function: receives SENSORY info from other neurons/receptors

Cell Body (soma/perikaryon)

-contains nucleus

-dendrites branch from cell body

-integrate input (decides whether or not to send signal)

-function: metabolism and synthesis for cell

axon hillock

-interface between axon and cell body

-function: generates action potentials

-part of cell body

axon

-conducts signal (action potential) from cell body to terminal boutons

-can be myelinated (impulses fast) or non-myelinated (slow)

terminal bouton

-specialized process for communication

-releases neurotransmitters when activated by action potential

Structures of Neuron: Function (Neuronal Zones)

Integration zone -> cell body

input zone -> dendrites

conduction zone -> axon

output zone -> axon terminals

single cell

info travels in ONE DIRECTION

neuron

axon of neuron

nerve fiber

-groups of fibers travelling together

-info can go EITHER DIRECTION

Nerve (PNS)

Tract (CNS)

Review slide

Review

Answers to review slide

Answers

supporting cells in the nervous system are called

neuroglia ("nerve glue")

neuroglia

-provide structural support

-form the myelin sheaths of axons and act as insulators and aid conduction velocity (fast conduction)

-control supply of nutrients across blood brain barrier

-maintenance: support and clear dead neurons

how do neuroglia differ from neurons?

1. neuroglia have NO ACTION POTENTIALS

2. neuroglia are able to DIVIDE

3. neuroglia do NOT FORM SYNAPSES

astrocytes functions

1. recycle neurotransmitters

2. secrete neurotropic factors (stimulate growth and maintenance)

3. maintain homeostatic balance in extracellular space

4. gatekeepers to CNS (line the blood brain barrier)

-smallest glial cells

-represent intrinsic immune cells of CNS

microglia

Oligodendrocytes functions

1. forms myelin sheaths in CNS

(around brain and spinal cord axons)

2. provide support to axons

myelin is not continuous cover, there are bare spots called

nodes of Ranvier

__________ are primary glia cells of the PNS

Schwann cells

Schwann cells

-one cell wraps around one axon

-membrane composed primarily of lipids (insulator that speeds transmission rate of action potentials)

difference in electrical charge inside and outside a cell which is at rest

resting membrane potential

most neurons have a resting membrane potential of

-65 to -70 mVolts

how is the negative charge maintained?

more negatively charged anions in intercellular space

-ion channels are membrane proteins that allow the passage of certain ions depending on size and charge

3 factors that maintain the negative charge of the resting potential

1. selectively permeable membrane

-large protein anions (negative) that can't pass through cell membrane to get outside of cell

2. ions moving toward equilibrium potential

-resting passive K+ channels allow K+ cations to pass through membrane into intracellular space

-concentration gradient pushes K+ out of cell

-balance (equilibrium) of forces reached (at -65mV)

3. Na/K pump (active)

-Na+ cations pumped out of cell against electrostatic and concentration gradients (leak into cell)

Na+ cations are actively moved to extracellular space by

Na+/K+ pump

Na+ has ___________ gradient and ____________ gradient forces

concentration, electrostatic

Na+ drives to _________ the cell

enter

___________ reduces Na+ concentration in cell

active pump

exchange ______ Na+ for ______ K+ coming in

3 Na+

2 K+

Na+/K+ pump is a _________ dependent process

ATP

ATP generation requires _________ and _______ but neurons do not store them

glucose

oxygen

anything that alters _______ or ________ will alter Na+/K+ pump effectiveness and produce neurological defects

glucose or oxygen

why is resting membrane potential important?

this electrical potential is stored energy required for neural communication -> action potential

_____________ is the basic mechanism for transmission of info in the nervous system and muscles

action potential

an action potential is caused by __________ of a membrane past a certain ___________ followed by ____________

depolarization

threshold

repolarization

an action potential is an __________________ response: only occurs if cell is depolarized past a threshold

"all-or-none"

propagation of action potential is a ______________ reaction

chain

AP at one site of axon causes ____________ adjacent to current AP, brings adjacent sites to _______________

depolarization

threshold

membrane potential becomes less negative (does not need to be positive)

-less negative when compared to resting membrane potential

depolarization

membrane potential (charge of cell) at which an action potential is inevitable

threshold

what happens when membrane potential becomes less negative

-cell can overshoot and be positive relative to outside

action potential occurs

membrane potential heads to original resting spot

repolarization

period where cell overshoots generally becoming more negative to resting potential

relative refractory period

during refractory period, neurons have __________ capacity to produce an action potential

diminished

period where no amount of stimulation can induce an action potential (immediately after action potential)

absolute refractory

period where a very strong stimulation can induce another action potential (not immediately after action potential, but prior to return to resting potential)

relative refractory

neurons encode intensity using this mechanism

"rate coding"

how does ion movement underlie changes in cell membrane potential?

1. depolarization

-stimulus results in slight positive charge, which allows some voltage-gated Na+ channels to open, leading to depolarization

2. if threshold reached, additional voltage-gated Na+ channels open, causing rapid change in charge

3. action potential is generated

-intracellular region becomes positively charged due to large influx of Na+ ions

4. Na+ channels now inactivated by gate terminates the AP and voltage-gated K+ channels open. The positive charges inside the cell force K+ cations out. Excess K+ channels open leads to a hyperpolarization (more negative cell membrane charge relative to resting state). Relative refractory state.

5. Cell membrane repolarizes and returns to resting potential. K+ charge reaches equilibrium with electrostatic and concentration gradients. cell membrane ready for another AP.

where is depolarization initiated?

spike-initiation zone

-> sensory nerve endings or axon hillock

change in membrane potential occurs in ___________ down the axon

one direction

-due to blockade behind it, it can't go backwards

-in absolute refractory period behind

membrane depolarizes in region __________ to action potential

adjacent

myelin sheath influences ________ of action potential conduction

speed

lipid insulator of neuronal axons

myelin

myelinated cells in PNS

Schwann cells

myelinated cells in CNS

oligodendrocytes

why can't an entire neuron be covered in myelin?

no place for current flow across membrane and no action potential

separation in myelin sheath

nodes of Ranvier

what are concentrated at the nodes of Ranvier?

voltage gated Na+ channels

nerve impulse jumps from node of Ranvier to node of Ranvier. this is called:

saltatory conduction

myelination causes nerve impulses to occur about _______ times faster than unmyelinated

50

__________ cells limit the locations where ion exchange can occur

Schwann

-specializations for communication

-site where info is transmitted from one cell to the next

-electrical or chemical

synapse

where does neurotransmission occur?

dendrites: spine

axons: boutons

one of the 3 components of a synapse that is the source of information

-signal can be chemical or electrical

-releases neurotransmitter

presynaptic neuron or nerve terminal

one of the 3 components of a synapse that is the target

-a dendrite, cell body, or target cell receiving the synaptic input

postsynaptic neuron

link between presynaptic and postsynaptic neuron in electrical signals

gap junction

link between presynaptic and postsynaptic neuron in chemical synapses

synaptic cleft

synaptic contact can occur on the dendrites, cell body, or terminal

-what are the 3 names?

axodendritic (majority)

axosomatic

axoaxonic

very fast transmission of synapse

-gap junction: proteins in membrane that form pores between 2 cells

-cells are "_________ coupled"

-flow of ions from cytoplasm to cytoplasm

electrical

(electrically)