Efferent Nervous System Flashcards
Preganglionic Neurons
Come from ventral NS to ganglion
- Multipolar cell body’s in the brain stem or spinal cord
- Axons are long + lightly myelinated
- End of the axon synapses on postganglionic neurons in ganglia
Postganglionic Neurons
Come from ganglion
Soma in gangilion to targets:
Smooth muscle, cardiac muscle, glands + adipose
Axons are short and unmyelinated so signal terminates at the target
Ganglia
Close to or on target organs
Autonomic Nervous System
Involuntary branch of the Efferent Nervous System that branches into two other systems: Sympathetic NS + Parasympathetic NS
Controls: smooth muscle, cardiac muscle, glands, adipose tissue
Antagonist control
Organs are controlled by sympathetic + parasympathetic NS for opposite effects.
Organs actions - come from the balance of signals from the 2 systems
Sympathetic Nervous System
(fight / flight / freeze)
Gets the body ready for action
Goes everywhere the parasympathetic goes
Also goes to: all blood vessels, skin, adipose + kidneys
Does several things that the parasympathetic doesn’t effect
Parasympathetic
Nervous System
(Rest + Digest)
Promotes normal body metabolism + upkeep.
Under most conditions the parasympathetic dominate.
Sympathetic + Parasympathetic effects on:
The heart
Sympathetic increases heart rate
Parasympathetic decreases heart rate
Sympathetic + Parasympathetic effects on:
The Lungs
Sympathetic dilated branches, increase airflow
Parasympathetic constricts branches, decreases airflow
Sympathetic + Parasympathetic effects on:
Digestive system glands, including salivary glands
Sympathetic inhibits secretion
Parasympathetic promotes secretion
Sympathetic + Parasympathetic effects on:
Smooth muscles of digestion
Parasympathetic promotes the movement of food through the digestive tract
Sympathetic inhibits
Sympathetic + Parasympathetic effects on:
The Liver
Sympathetic promotes the release of glucose from glycogen
- Glycogen → glucose
- Frees up glucose for body use
- Promotes breaking down for food
Parasympathetic: glucose → glycogen
- Stores glucose for later use
Sympathetic + Parasympathetic effects on:
The Bladder
Parasympathetic: promotes urination
Sympathetic: inhibits
Sympathetic + Parasympathetic effects on:
Eyes
Symp: dilates pupil - bigger
- Relaxes lens muscles so you can focus far away
- Does nothing
Para: constricts pupil - narrower
- Contracts lens muscles so you can focus up close
- Promotes secretion of tears from lacrimal gland
Dural innervation
Organ is signaled by the sympathetic + parasympathetic.
Anatonists have the opposite effects
Autonomic Ganglia
Where the 1st neuron signals the 2nd neuron
Divergence
Occurs when around autonomic ganglia each neuron coming in signals many neurons coming out
More neurons coming out than ganglia
Sympathetic Tone
Sympathetic NS is always stimulating every blood vessel to constrict. Can decrease for dilation or increase stimulation - so it constricts more
Sympathetic NS relationship with kidneys
Sympathetic inhibits urine production
Promotes secretion of renin = hormone that raises blood pressure
Sympathetic NS relationship with blood vessels
Makes the smooth muscle in all blood vessels contract and some in the skin to relax.
Constricts + narrow blood vessel
- Raises blood pressure
- Moves blood to other parts of the body
Sympathetic NS relationship with adipose
makes adipose break down fat for energy
Sympathetic NS relationship with skin
- Makes arrector pili muscles contract - gives goosebumps
- Promotes sweating from sweat glands
- Blood vessels in the skin
Flight, Fight, or Freeze
Sympathetic NS relationship with the adreanal gland
Promotes the release of epinephrine + norepinephrine from the adrenal medulla.
Epinephrine = adrenaline + Norepinephrine released into blood
- Wide-ranging effects throughout body
- Promotes catabolic metabolism in many cells throughout the body (break down molecules for energy)
Sympathetic NS relationship with preganglionic neurons from thoracic + lumbar vertebrae
- Ganglia next to the spinal cord
- Short lightly myelinated preganglionic neurons
- Long unmyelinated postganglionic neurons
Somatic Motor Neuron
Only kind of neuron in the Somatic NS, connects the CNS to skeletal muscle.
- Soma in grey matter of brain stem on spinal cord (ventral horn)
- Long highly myelinated axon
- Ends of axons branch a lot inside of a skeletal muscle organ
Signaled from cells in cerebral cortex + other neurons
→Exists CNS on all spinal nerves + most cranial nerves
→ Innervate many skeletal muscle fibers - in a motor unit
→Release ACh → binds nicotonic receptors on muscle → muscle depolarizes → muscle AP → muscle contracts
Travels down somatic motor neuron terminals
Somatic
Neuromuscular Junction
Synapses on each skeletal muscle fiber
Makes those fibers contract
Like synapses - at the end of each branch of axon
Acetylcholine (ACh)
The primary neurotransmitter in the efferent NS that go to 2 types of receptors:
Nicotonic + Muscarinic receptors
Secreted into the NS by cholinergic neurons.
Cholinergic neuron
Neuron that secretes ACh for:
- Somatic motor neurons
- Preganglionic neurons in sympathetic + parasympathetic NS
- Parasympathetic postganglionic nerves
+ Many neurons in the CNS
Nicotonic Receptor
Ligand lated NA+ Ca++ ion channels that open in response to ACh.
- Always excitatory
- Nicotine is an agonist
Receptors are in the Efferent NS
- On skeletal muscle fibers - somatic motor neurons release ACh
- Binds nicotonic receptors on muscles
Preganglionic neurons
- Postganglionic neurons release in the ganglia
- Binds nicotonic receptors on postganglionic neurons
Muscarinic receptors
G-protein coupled receptors (GPCR). Usually open + close K+ & Ca++ channels but when postganglionic parasympathetic neurons release ACh on targets, ACh binds muscarinic receptors onto targets.
- Targets parts of parasympathetic NS
- Act as secondary messengers to other effects
- Also have a metabolic effect
- Excitatory or inhibitory
Norepinephrine
in the Efferent NS
Neurotransmitter released by sympathetic postganglionic neurons on their targets
Epinephrine - a very similar chemical aka adrenaline
Adrenergic Neurons
Are sympathetic postganglionic neurons that release norepinephrine or epinephrine - Many neurons in the CNS
What is the relationship with adrenal medulla and norepinephine?
Middle of the adrenal gland that releases epinephrine + norepinephrine into the blood as hormones, gives a general effect all throughout the body.
Signaled by preganglionic cells of sympathetic NS
Adrenergic receptors & types
Receptors for epinephrine + norepinephrine
1. Alpha receptors
2. Beta receptors
3. Many sub types
All GPCRs - can have many effects
- Effect depends on what type of receptor a cell has
- - Some make blood vessels constrict
- - Others make blood vessels dilate
All receptors respond to epinephrine + norepinephrine - some respond more to 1 than the other.
Motor control by the Efferent NS does…
NS uses many sensory inputs to plan motor actions
Processed consciously in the cerebral cortex
Processed unconsciously in other parts of CNS
Efferent NS
Motor Control
Anatomy
- Premotor cortex
- Primary motor cortex
- Cerebellum
- Basal ganglia
- Giant pyramidal neurons + their tracks
- Motor neurons that leave the CNS to make muscles contract
Premotor cortex
Plans complex motions involving multiple muscle groups
Receives signals from sensory cortices + association areas
Primary motor complex
- Directly controls somatic motor neurons
- Has a homunculus = map of the body
Neurons in part of the map fire → muscles corresponding contract - Receives signals from premotor cortex
Cerebellum
Helps generate smooth + coordinated motions by comparing the motor complex plan to what is actually going on.
- Gets signals from the motor cortex
Somatic senses - especially proprioception + vestibular sense
- Sends signals back to the motor cortex
Basal ganglia
Receive signals from all parts of the cortex to help coordinate motor actions. Then sends signals back to the premotor complex
At default, it suppresses cortex from generating motions
Most release suppression to move
Giant Pyramidal Neurons
Have:
Cells bodies are in the primary motor complex
Axons going down the spinal cord
Synapse on somatic motor neurons in the spinal cord
Run on pyramidal tracks
Pyramidial Tracks
White matter tracks that pyramidal axons travel down the spinal cord on.
- Ventral
- Direct = cortext to→ motor neurons
Autonomic NS &
The Brain Stem
The brain stem controls many autonomic reflexes:
1. Cardiovascular center
2. Respiratory centers
3. Other centers control the digestive tracts
- Neurons in the brain stem synapse on presynaptic neurons in the brain stem + spinal cord
Autonomic NS &
Hypothalamus relationship
Hypothalamus is the primary integration center for the Autonomic NS.
Regulates homeostasis - largely through the autonomic NS
Gets signals from the visceral senses
Anterior controls parasympathetic + Posterior controls sympathetic
Neurons in the hypothalamus synapse on preganglionic neurons in the brain stem
Autonomic NS &
Cortex
Doesn’t directly control the autonomic ns but can effect emotions. Emotional effect comes indirectly through the limbic system.
Parasympathetic Nervous System Anatomy
Ganglia throughout the body
Cranial nerves: III, VII, IX
Vegas nerve
Sacral nerves: S2, S3, S4
