Chapter 4.2 Peripheral Nervous System ✓ Flashcards
What is the role of the peripheral nervous system?
PNS takes messages from receptors to the CNS and from the CNS to muscles and glands
What does the PNS consist of?
It consists of:
-Nerve fibres that carry information to and from the CNS
-Groups of nerve cell bodies, called ganglia, which lie outside the brain and spinal cord.
Define cranial nerve
Cranial nerves are one of the 12 pairs of nerves that arise from the brain
What are some examples of cranial nerves?
-Optic nerve
-Auditory nerve
What does it mean for a cranial nerve to be a mixed nerve?
It means the nerve can contain both sensory and motor nerve fibres
What types of fibres do mixed cranial nerves contain?
They contain sensory fibres (carrying impulses into the brain) and motor fibres (carrying impulses away from the brain).
What are sensory fibres?
Sensory fibres are fibres that carry impulses into the CNS
What are motor fibres?
Motor fibres are fibres that carry impulses away from the CNS
Define spinal nerves
Spinal nerves are one of the 31 pairs of nerves that arise from the spinal cord
Why are spinal nerves considered mixed nerves?
Because they contain both motor and sensory fibres
Are all cranial nerves mixed nerves?
No, some are just are purely sensory, some are purely motor, and others are mixed.
How is each spinal nerve connected to the spinal cord?
By two roots: the ventral root and the dorsal root.
What does the ventral root of a spinal nerve contain?
The axons of motor neurons.
Where are the cell bodies of motor neurons located?
In the grey matter of the spinal cord.
What does the dorsal root of a spinal nerve contain?
The axons of sensory neurons.
Where are the cell bodies of sensory neurons located?
In the dorsal root ganglion, a small swelling on the dorsal root.
How many pairs of cranial and spinal nerves is the PNS made up of?
12 pairs of cranial nerves and 31 pairs of spinal nerves
What are the two divisions of the PNS?
The afferent and efferent division
Define the afferent division
The afferent division contains sensory neurons that transmit impulses from sensory receptors (in the skin, muscle and internal organs) to the brain and spinal cord, where in information is processed.
What another word for the afferent division?
the sensory division
What does the afferent division divide into?
Somatic and visceral sensory neurons
Define the role of somatic sensory neurons
They bring impulses from the skin and muscles
Define the role of visceral sensory neurons
They bring impulses from the internal organs
Define the efferent division
The efferent division contains nerve fibres that carry impulses out of the brain and spinal cord
What another word for the efferent division?
motor division
What does the efferent division divide into?
Somatic and autonomic division
Define the role of the somatic division
It takes impulses from the CNS to the skeletal muscles
Define the role of the autonomic division
It takes impulses from the CNS to heart muscle, involuntary muscles and glands
What does the autonomic division divide into?
Sympathetic and parasympathetic division
What is the main function of the sympathetic division?
It prepares the body for stress, emergencies, or high activity (“fight or flight”).
What are the main functions of the parasympathetic division?
It promotes relaxation, energy conservation, and homeostasis (“rest and digest”).
Define autonomic nervous system (ANS)
The ANS controls the body’s internal environment and is involved in many of the mechanisms that keep it constant.
What regulates the autonomic nervous system?
Groups of nerves cells in the medulla oblongata, hypothalamus and cerebral cortex
What are some of the body functions regulated by the ANS (9)?
-Heart rate
-Blood pressure
-Body temperature
-Digestion
-Release of energy
-Pupil diameter
-Air flow to the lungs
-Defecation
-Urination
What is the role of the nerve fibres of the ANS?
They carry impulses to the heart muscle, other muscles of the internal organs and the glands
How do impulses travel in the ANS?
Impulses travel along two neurons:
-First neuron extends from the CNS to a ganglion
-Seconds neuron extends from the ganglion to the target effector (heart, glands, or smooth muscles)
How are the two neurons in the ANS structured?
-First neuron is myelinated and releases acetylcholine at the ganglion
-Second neuron is unmyelinated and releases either acetylcholine or noradrenaline depending on whether its part of the parasympathetic or sympathetic division
What happens to heart rate during a sympathetic response?
Increases to pump more blood to muscles.
How does the parasympathetic system affect heart rate?
Decreases heart rate to maintain a resting state.
How does the sympathetic nervous system affect the lungs?
Dilates bronchioles to increase airflow.
How does the sympathetic nervous system affect the liver?
Increases glycogen breakdown to release glucose.
What happens to the pupils during sympathetic activation?
Dilate to improve vision.
How does the sympathetic system affect sweat glands?
Increases sweat secretion to cool the body.
How does the parasympathetic nervous system affect digestion?
Increases movement in the stomach and intestines.
How does the parasympathetic nervous system affect saliva production?
Increases secretion of saliva
What happens to the pupils during parasympathetic activation?
Constrict to reduce light intake.
How does the sympathetic nervous system affect the heart?
Increases heart rate and strength of contraction.
How does the parasympathetic nervous system affect the heart?
Decreases heart rate and strength of contraction
How does the parasympathetic nervous system affect the lungs?
Constricts bronchioles to reduce airflow.
What is the effect of sympathetic stimulation on digestion?
Decreases movement (reduces digestion).
What does the parasympathetic nervous system do to the liver?
Increases glucose uptake and glycogen synthesis (stores energy).
How does the parasympathetic system affect sweat production?
No effect (sweat glands are mostly controlled by the sympathetic system).
What happens to saliva secretion during sympathetic activation?
Decreases saliva production.
How does the sympathetic system affect blood vessels in the skin?
Constricts them to reduce blood flow to the skin.
How does the sympathetic system affect blood vessels in skeletal muscles?
Dilates them to increase blood flow to muscles.
What does the sympathetic nervous system do to the bladder?
Relaxes bladder muscles (reduces urination).
What does the parasympathetic nervous system do to the urinary bladder?
Contracts bladder muscles (increases urination).
How does the sympathetic nervous system affect the adrenal medulla?
Stimulates hormone secretion (releases adrenaline and noradrenaline).
How does the parasympathetic nervous system affect the adrenal medulla?
No effect (only the sympathetic system controls it).
What is the overall difference between the sympathetic and parasympathetic nervous systems?
The sympathetic system prepares the body for fight-or-flight, while the parasympathetic system helps the body rest and digest.
