test 3 Flashcards
Two anatomical divisions of the nervous system
- Peripheral nervous system
* Nerve fibers that carry information between periphery and CNS - Central nervous system
* Brain
* Spinal cord
The Central Nervous System: brain
- Processes input and output
* Analogous to a computer CPU
The Central Nervous System: spinal cord
• Conduit for signals between the body and the brain
The Peripheral Nervous System: Efferent Division
- Carries signals away from the CNS to peripheral tissues
* “E” = Exits
The Peripheral Nervous System: Afferent Division
- Carries sensory information from the periphery to the CNS
* “A” = Arrives
The Afferent Division of PNS
- Provides sensory input to modulate the function of the efferent division
* Reflex arcs
* Neural pathways that mediate a reflex action
The Efferent Division of PNS: Autonomic nervous system
- Unconscious regulation of everyday bodily functions
- Visceral
- Vegetative
- Involuntary
The Efferent Division of PNS: Somatic nervous system
• Conscious control of skeletal muscles
The Somatic Nervous System
- The voluntary branch of efferent nervous system
- Consists of sensory and motor neurons
- Sensory Neurons
* Transmit messages to CNS - Motor neurons
* Supply the skeletal muscles
* Cell bodies located in spinal cord
* Axon is continuous from spinal cord all the way to the skeletal muscle
* Terminates at neuromuscular junction
* Can only stimulate, not inhibit
The Neuromuscular Junction
• Motor neuron axon terminals release acetylcholine from vessicles due to the influx of Ca++ which causes the vessicles to fuse with the membrane wall releasing ACh into the synaptic cleft
-ACh that binds to receptors allowing ions (Na) to come in depolarizing the muscle
• Acetylcholine (ACh) brings about excitation and contraction of skeletal muscle
• Acetylcholinesterase (AChE) terminates acetylcholine activity at the neuromuscular junction
The Autonomic Nervous System (ANS)
- Coordinates regulation and integration of bodily function with the endocrine system
- Rapid transmission of electrical impulses along nerve fibers to effector cells
- Effector cells secrete neuromodulator substances
- Endocrine system funcitons via hormonal signals
- ANS functions via electrical impulses and neurotransmitters
ANS Divisions
- Enteric ->“Brain of the Gut”
- Parasympathetic (PNS) -> “Rest & Digest”
- Sympathetic (SNS) -> “Fight or Flight”
Somatic nervous system
- myelinated neurons
- ACh affecting skeletal muscle contrations
Autonomic nervous system affects 3 specific areas of the body
- either ACh or NE
- smooth muscle - contractions or relaxation
- cardiac muscle - increases or decreased rate and force of contraction
- glands - increase or decreased secretions
ANS Motor Neuron Pathway
- Efferent division carries nerve impulses which EXIT the CNS
- Two types of neurons connecting at the ganglia
* Preganglionic
* Postganglionic
Preganglionic Neurons
- Cell body located within the CNS
* Emerge from brainstem or spinal cord and make a synaptic connection in ganglia
Postganglionic Neurons
- Cell body originates in the ganglion
* Terminates on the effector organs
Efferent Neurons of the ANS
- Parasympathetic and Sympathetic neurotransmitter substances
* Both preganglionic sites: ACh
* Parasympathetic postganglionic site: ACh
* MOST sympathetic postganglionic sites: Norepinephrine (NE) - Parasympathetic neurons arise from cranial nerves and sacral region (cranial-sacral division)
- Sympathetic neurons come from thoracic and lumbar regions (thoraco-lumbar region)
Parasympathetic pre and post ganglionic length
- Pre: very long
- Post: very short
sympathetic pre and post ganglionic length
- Pre: very short
- Post: long
The Enteric Nervous System
- Collection of nerve fibers that innervate
* GI tract
* Pancreas
* Gallbladder - Functions independently of CNS
- 2 components
* Myenteric plexus (Plexus of Auerbach)
* Submucosal plexus (Plexus of Meissner)
The Sympathetic Nervous System
- Continually active
* Vascular tone - Adjusts in response to stressful situations
* Trauma
* Fear
* Hypoglycemia
* Cold
* Exercise - Direct sympathetic activation of effector organs
- Stimulation of adrenal medulla to release epinephrine and norepinephrine
- Response is diffuse (everything becomes activated at the same time)
The Sympathetic Nervous System Effect of stimulation
- Increase heart rate
- Increase blood pressure (almost exclusively controled by SNS)
- Mobilize energy stores
- Increase blood flow to skeletal muscles
- Increase blood flow to the heart
- Dilation of pupils
- Dilation of bronchioles
The Parasympathetic Nervous System
- Maintains homeostasis
- Decreases
* decrease Heart rate
* decrease Diameter of airways (bronchoconstriction)
* Diameter of pupils (constriction) - Conserves and restores energy during times of rest
* S alivation
* L acrimation
* U rination
* D igestion
* D efecation - Discrete response (don’t get all of the actions at once because of the minimal branching)
ONLY sympathetic stimulation to these organs
• Sweat glands • Adrenal medulla • Kidney • Pilomotor muscles -Blood Pressure is Controlled Almost Exclusively by the Sympathetic Nervous System
Can Strong emotions can modify the activity of the ANS
-yes
• Rage
• Fear
• Pleasure
Chemical Signaling Between Cells: Hormones
- Specialized endocrine cells secrete hormones into bloodstream
- Exert effects on broadly distributed target cells
Chemical Signaling Between Cells: Local mediators
• Secreted by most cells in the body • Act locally -act on cell itself or nearby cells • Destroyed quickly • Do not enter bloodstream
Chemical Signaling Between Cells: Neurotransmitters
- Released by nerve cells
- Between nerve cells
- Between nerves and effector organs
Hormones, Local Mediators and Neurotransmitters all Bind to Specific Receptors on Target Cells because
- Too hydrophilic to penetrate the membrane
* Signal mediated through receptor binding
Another name for the parasympathetic nervous system
- cholinergic nervous system
- uses ACh
Another name for the sympathetic nervous system
- adrenergic nervous system
- uses epi and NE
Types of Neurotransmitters
- Although often referred to as the cholinergic nervous system and the adrenergic nervous system, there are A LOT of other neurotransmitters involved
* For example: dopamine, serotonin, histamine, glutamate - Acetylcholine and norepinephrine are primary neurotransmitters in the ANS
Acetylcholine (ACh)
- If transmission is mediated by ACh, the neuron is labeled cholinergic
- Mediates transmission
* Sympathetic ganglia
* Parasympathetic ganglia
* Adrenal medulla
* Parasympathetic postganglionic nerves to effector organs
* Few sympathetic system organs (sweat glands) (during fight or flight to cool our body temperature down)
* Neuromuscular junction (somatic system)
types of cholinergic receptors
- Nicotinic
* Muscarinic
Norepinephrine & Epinephrine
• If transmission is mediated by norepinephrine or epinephrine, the neuron is labeled adrenergic
Adrenergic Receptors
- α-adrenergic
* α1
* α2 - β-adrenergic
* β1
* β2
Autonomic function is integrated into the central nervous system
• At midbrain and medulla there is integration of:
• Endocrine system
• ANS
• Sensory input
• Higher CNS centers including cerebral cortex
• Important cooperative interactions between parasympathetic and sympathetic systems
-combining all of the information from all of the systems to produce the appropriate response
The primary controlled variable in cardiovascular function is
- mean arterial pressure
• Anything that changes MAP can and will have a powerful secondary (reflex response)
• For example: Autonomic drugs!!
-NE drug given which should increase HR
-the HR actually decreases because of the baroreceptors fire as BP increases causing a negative feedback resulting in decreased sympathetic outflow to the heart
-powerful increase in parasympathetic output to the heart (Vagus nerve at cardiac pacemaker)
-SO NET EFFECT OF NE
=increase in SVR
increase in MAP
decrease in HR
but only when reflexes are intact
Presynaptic Regulation (so we don’t have over-activation
- Presynaptic feedback inhibitory control mechanisms have been shown to exist at most nerve endings
- Autoreceptor
- Heteroreceptor
Autoreceptor
- Neuron has receptors on it that will respond to the chemical that it is releasing (example: norepinephrine)
- Usually inhibitory
Heteroreceptor
• Neuron responds to chemicals released from other neurons nearby that synapse with the nerve ending
Postsynaptic Regulation
- Up-regulation or down-regulation of receptors based on the history at the receptors (decensitization)
- Modulation by events evoked by the same or other transmitters acting on different postsynaptic receptors (an additive affect from an excitatory and inhibitory transmitters resulting in not too much excitement)
