PNS and Efferent

what is the pathway for efferent (motor) pathway?

somatic and autonomic pathway

where does somatic pathway lead to?

motor neurons to skeletal muscles

where does autonomic pathway lead to?

parasympathetic and sympathetic to glands and cardiac and smooth muscle

what is a reflex?

•Rapid, preprogrammed, involuntary reaction to a stimulus

•Involves few nerves and synapses

•Less synapses = less synaptic delay

•Fast response

•Neural reflexes can be classified many ways

what is a monosynaptic reflex?

Direct communication between sensory and motor neuron

(e.g., stretch reflex)

what is a polysynaptic reflex?

Interneuron facilitates sensory-motor communication

(e.g., withdrawal reflex

what is a somatic reflex?

ex. withdrawal reflex; immediate response

what is an autonomic reflex?

adjust activity of smooth muscle & cardiac muscle contractions, or secretions by glands

•Rapid responses to correct

fluctuations in homeostatic conditions

what is the goal of sympathetic and parasympathetic pathways?

• maintain homeostasis

• innervate cardiac and smooth muscle, most exocrine glands and some endocrine glands

what is the purpose of sympathetic pathways?

• fight or flight

• prepare body to deal with stress or increased activity while still maintaining homeostasis

what is the purpose of parasympathetic pathways?

• rest and digest

• maintain homeostasis during times of less activity

• conserve energy and replace energy stores (glycogen and fat)

what are the neurons for the autonomic nerve pathway?

• preganglionic fiber

• postganglionic fiber

what are the characteristics of parasympathetic division?

• little branching

• innervates few effector tissues

what are the characteristics of sympathetic division?

• lots of branching

• innervates many effector tissues

how does the parasympathetic pathways control organs and tissues?

•Stimulates few structures at one time

•Can respond to local changes in homeostatic conditions

•Doesn’t turn everything on all at one time

how does the sympathetic pathway control organs and tissues?

•Stimulates many structures simultaneously

•“mass activation”

•Coordinates rapid changes in the body all at once

what are the 2 main neurotransmitters?

• acetylcholine (ACh)

• norepinephrine (NE)

what is the autonomic nerve pathway?

CNS → preganglionic fiber → preganglionic neurotransmitter → autonomic ganglion → postganglionic fiber → post ganglionic neurotransmitter → effector organic

what is the preganglionic neurotransmitter in both sympathetic and parasympathetic pathways?

acetylcholine (Ach)

what is at the end of the postganglionic fiber?

varicosities (enlarged swellings)

what do neurotransmitters do?

• stimulate or inhibit activity in cells

• response depends on the type of receptors on the tissue cells (target cells_

what are the types of autonomic receptors?

• cholinergic receptors

• adrenergic receptors

what are the types of cholinergic receptors?

• nicotinic receptors

• muscarinic receptors

what do cholinergic receptors do?

bind to Ach

what do adrenergic receptors do?

bind to NE and epinephrine

what are the types of adrenergic receptors?

• alpha receptors

• beta receptors

what do nicotinic receptors do?

stimulate

what do muscarinic receptors do?

(can stimulate or inhibit, depending on the

    effector tissue)

–Smooth muscle of

   digestive tract  (stimulate)

–Cardiac muscle

   (inhibit)

what do alpha 1 receptors do?

–α₁ stimulate in general

(smooth muscle in most blood vessels)

what do alpha 2 receptors do?

Inhibit smooth muscle of digestive tract

what do beta 1 receptors do?

stimulate (heart)

what do beta 2 receptors do?

–inhibit (smooth muscle in blood vessels supplying heart, skeletal muscle)

what is the parasympathetic pathway

preganglionic axon releases Ach → Ganglionic neuron cell body and dendrites always contain receptors for ACh. → postganglionic axon releases Ach or NE → target cells contain either Ach receptors or NE receptors

which nervous system dominates during stress (fight or flight)

sympathetic

what are the effects of fight or flight?

–pupils of the eye dilate

–sweating

–heart rate increase

–bronchioles dilate

–motility for digestion is inhibited

–liver: conversion of glycogen into glucose

–urine production is inhibited

what is the adrenal medulla?

a modified part of the sympathetic nervous system

what does the adrenal medulla do?

•Produces norepinephrine (20%) and epinephrine (80%)

•Releases them into the blood as hormones instead of as messengers to postganglionic fibers

•Reinforces the effect of the sympathetic nerve pathways

which nervous system dominates during rest and digest?

parasympathetic

what are the effects of rest and digest?

–Intestinal motility for digestion is increased

–Blood flow to kidneys and urine production is increased

–Pupils constrict

–Heart rate, force and pressure decrease

do most orangs innervate between parasympathetic and sympathetic pathways?

yes

which pathways are in most arterioles and veins?

sympathetic

which pathway is in sweat glands?

sympathetic

which pathways are in salivary glands?

both parasympathetic and sympathetic

what is black widow spider venom?

venom triggers explosive release of Ach from storage vesicles

how does black widow spider venom work?

•Causes all cholinergic sites to undergo prolonged depolarization resulting in respiratory failure due to paralysis (depolarization block)

what is botulinum?

toxin causes the blocking of release of Ach from terminal ends in response to action potential

how does botulinum work?

•Prevents muscles from responding to nerve impulses, causing death due to respiratory failure by the inability of the diaphragm to contract

•Lethal dose is less than 0.0001mg

what is curare poison?

reversibly binds to Ach receptor sites on the motor end plate.

how does curare poison work?

•When bound, the Ach can’t bind and the channels don’t open to alter membrane permeability

•Muscles don’t respond to nerve impulses causing paralysis

•When high enough concentration to block enough Ach receptors a person dies from respiratory paralysis due to inability of the diaphragm to contract

what is the neuromuscular junction?

•Similar to synapse in neuron, but:

–Na+ influx causes depolarization to affect adjacent areas

–ap propagated in both directions

–One-to-one transmission of ap in neuron causes ap in muscle cell (no summation required)