Somatosensory Paths

Sensory info enters through _____ nerves and is sent to?

peripheral nerve

All levels of spinal cord

Reticular substance of medulla, pons, mesencephalon, cerebellum, thalamus, cerebral cortex

Skeletal motor paths

-controls?

What brain areas affect control?

bodily activities

-contraction of muscles

-secretion of exocrine and endocrine glands

Spinal cord, reticular substance of medulla, pons, mesencephalon, cerebellum, basal ganglia, motor cortex

Regions of motor control in CNS

Higher-Cortical

functions?

without cortex fxns of ____ are imprecise

deliverate movement

memory

never fxns alone, always in association with lower centers of the NS

lower centers of NS

Regions of Motor control in CNS

Lower-Subcortical

Fxns?

subconscious activities: respiration, control of arterial pressure, equilibrium, feeding and emotional behaviors

Automatic and instantaneous motor response to sensory stimuli

Regions of Motor control in CNS

Spinal cord

Fxns?

walking movement

reflexes that withdraw body from painful objects

reflexes that stiffen the legs to support the body

reflexes that control bld vessels, GI movements, urinary secretion

(somatic and visceral reflexes)

blocked in transmission

changed from single to repetitive impulses

integrated with impulses from other neurons

neuron secretes substance like NT

NT acts on receptor proteins in membrane of next neuron. this excites, inhibits or modifies sensitivity

(Ach, Hist, GABA, glycine, 5HT, GLU)

electrical synapses

how do they work? what do they use?

direct open fluid channels - conduct electricity from cell to cell

GAp jxns: free movement of ions from interior of one cell to the next

(not many in CNS, many in visceral smooth muscle, cardiac)

Presynaptic terminals

located?

effect on postsynaptic terminal?

surface of dendrites and soma of motor neuron (not many on soma)

can have excitatory or inhibitory action

size of cell body

length, size or # of dendrites

length and size of axon

# of presynaptic terminals

Presynaptic Terminals

what are the 2 internal structure important to fxn of synapse?

transmitter vesicles (transmitter substance)

Mitochondria (provide ATP which is used to synth new transmitter substance)

Presyn membrane contains vg Ca channels

AP depolarizes membrane (Na channels open, Na enters cell), this causes opening of Ca channels, Ca flows into presynaptic terminal. (Amt of transmitter tha enters cleft is directly related to number of Ca ions that enter)

Ca binds w/ proteins, releases sites where vesicles containing NT bind. Vesicles open to exterior via exocytosis

Receptor Proteins

Located where?

Can use ___ or ___ to transmit signal?

postsynaptic neuron membrane

Ion channel or 2nd messenger

Receptor Proteins

- How does an excitatory NT work at the receptor protein?

How does an inhibitory NT work at the receptor protein?

Excitatory Nt OPENS CATION channel - allows Na into cell - excitation of postsynp neuron

Inhib NT opens anion channel - allows negative charges to enter - inhibits postsynaptic neuron

ion channels close quickly and are not suitable for causing prolonged changes to postsynaptic neuron

alpha, beta and gamma portions

Alpha is activator portion

when activated alpha separates form beta and gamma

alpha opens specific ion channels in postsynaptic membrane

activates cAMP or cGMP in neuronal cell

actiavtes one or more intracell enzyme

activates gene transcription

what are the mechanisms causing excitation? (ions)

inhibition?

opening Na channels - allows positives into cell

Lowering conduction through Cl- or K+ channels

opening Cl channels through receptor molecule

increase conductance of K through receptor

activate receptor enzymes (inhibitory)

synaptic transmitters

small molecule, rapidly acing transmitters

what kind of response?

transmit what signals where?

synthesized where?

recycled or not?

acute response

transmission of sensory signals to brain

motor signals to muscles

synthesized in cytosol of PRESYNAPTIC terminal

recycled

synaptic transmitters

neuropeptides

what kind of action?

sythesized where?

more or less potent than smaller transmitters?

recycled?

examples? (general)

Actions?

prolonged actions

-long term opening/closing of ion channels

-changes in number or size of synapses

Synthesized by ribosomes in cell body

released in smaller amt, more potent

NOT recycled

Hormones, growth factors

Porlonged closure of Ca pores

prolonged changes in activation/deactivation of genes

prolonged alterations in #s of excit/inhib receptors

Resting potential of spinal motor neuron

why important?

-65 mv

allows both positive and negative control of the degree of excitability of the neuron

-decreasing voltage to less negative makes membrane more excitable, increasing voltage to more negavite makes neuron less excitable

Synaptic mechanism

How is an EPSP generated?

Excitatory Nt released

increases membranes permeability to NA

Na diffuses to inside of cell

Causes membrane potential to rise from -65 to -45

if EPSP enough, AP elicited

what is an IPSP

what causes it?

increase in negativity beyond normal resting membrane potential

Caused by: Opening of Cl- channels, or K efflux (post synaptic inhibition) (hyperpolarization)

GABA released, anion channels opened

Cl- diffuses into cell

Cell more negative

Cancels effects from Na from AP

one terminal creates an EPSP of .5-1

Many presynaptic terminal usually stimulated at the same time

Effects summate and cause an AP

one terminal fires. Takes 15 ms to come back to resting potential

if same terminal fires quickly enough it would add to the effect of the first firing if done quickly enough

So... successive discharges from the same presynaptic terminal summate the reach threshold

Facilitation

How does it work?

one terminal fires and brings potential near threshold but not to it

has facilitated the neuron

next terminal fires

easier for it to reach threshold

dendrites lack vg Na channels, so dendrites cannot generate an AP themselves

They transmit an electric current down to soma.

Lose EPSPs down the axon before it reaches the soma

Reason: they are permeable to K and Cl making them leaky to electrical current

Decrease in membrane potential as it spreads down dendrites

Fatigue

Reasons?

after overstimulation neurons wear out

Reason:

has not had time to reporlarize

depletion of NT

inactivation of postsynaptic receptors

development of abnormal ion [ ]s in postsynaptic membrane