BI0005 - Lecture 2 - nerves 2
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What is the CNS?
The central nervous system - the brain and the spinal cord
What is the PNS?
What are the two distinctions of the PNS?
- The Peripheral nervous system - the nerves and ganglia of the body.
- Somatic - Controls the musculo-skeletal system
- Visceral - Controls the body's organs (autonomic nervous system)
What is Innervation?
The nerve supply of something
What is a motor neuron?
A neurone which causes movement
What is a sensory neurone?
A neurone which responds to a stimulus
What are afferent neurones?
Neurones which bring sensory information from the PNS to the CNS
What are efferent neurones?
Neurones which carry off information from the CNS to muscles, glands, and the endocrine cells.
What does the Somatic nervous system do?
In what way does it work?
- Controls the contraction of the skeletal muscles of the body
- i.e. somatic motorneurones are efferent neurones sending nerve impulses (action potentials) which cause muscle contractions.
Motorneurones don't cause muscle contraction spontaneously - they do so in response to a command. The action of most
motor neurones is a voluntary one
What are stereotyped movements?
Simple, repetitive movements - parkinsons disease thumb rubbing
What are non-stereotyped movements?
Complex movements individual to each person - hand writing.
What exerts control over (commands) motor neurones?
The Central nervous system
What is the ANS?
The autonomic nervous system - this regulates the internal environment by controlling smooth and cardiac muscles and the organs of the digestive, cardiovascualar, excretory, and endocrine systems.
What three divisions make up the autonomic nervous system?
The sympathetic division, parasympathetic division, and enteric division.
What is the sympathetic division?
- The sympathetic division corresponds to arousal and energy generation (the fight-or-flight response)
- e.g. the heart beats faster, digestion is inhibited, the liver converts glycogen to glucose, and secretion of epinephrine from the adrenal medulla is stimulated
What is the parasympathtic divisions?
- The parasympathetic division generally causes opposite responses (to the sympathetic division) that promote calming and a return to self-maintainance functions ("rest and digest")
- e.g. lowers heart rate,. enhances digestion, increases glycogen production
The sympathetic and parasympathetic divisions of the autonomic nervous system have largely ... functions in regulating organ function
What is the enteric division?
- The enteric division of the PNS consists of networks of neurons in the digestive tract, pancreas, and gallbladder.
- Within these organs, neurons of the enteric division control secretion, and they also control the smooth muscles that produce peristalsis.
- It is normally regulated by the sympathetic and parasympathetic divisions.
What does the sympathetic nervous system do to the eyes, the heart, the lungs, and the bladder?
- Dilates pupils
- Speeds up heart rate
- Dilates bronchi
- Inhibits urination
What does the parasympathetic nervous system do to the eyes, the heart, the lungs, and the bladder?
- Constricts pupil
- Slows down heart rate
- Constricts bronchi
- Stimulates urination
What could happen following an injury to the spinal cord?
If the control that the CNS has over the ANS is damaged (removed), perhaps following an injury to the spinal cord, a rapid rise in blood pressure follows that can cause a stroke or even be fatal.
What are the main parts of the cerebral hemispheres?
- The cerebral cortex
- The motor nuclei
- The Thalamus
- The Hypothalamus
Where in the brain is information processing largely centered?
In the Cerebrum.
What is the cerebrum divided into?
- The cerebrum is divided into right and left cerebral hemispheres.
- Each hemisphere consists of an outer covering of grey matter, the cerebral cortex; internal white matter; and groups of neurons collectively called basal nuclei that are located deep within the white matter.
What does the cerebellum do?
- Coordinates movements and balance.
- receives sensory information about the positions of the joints and the length of the muscles, as well as input from the auditory and visual systems.
- Also monitors motor commands issued by the cerebrum
- Hand-eye coordination is an example of cerebellar control; if the cerebellum is damaged, the eyes can follow a moving object, but they will not stop at the same place as the object
What does the brainstem do?
It functions in homeostasis, coordination of movement, and conduction of information to and from higher brain centers.
All axons carrying sensory information to and motor instructions from higher brain regions pass through the brainstem.
What does the brainstem consist of?
- Midbrain - connected to the cerebral hemisphere
- The pons - major connections with the cerebellum
- The medulla (oblongata) - connected to the spinal cord
The CNS is divided into ... matter and ... matter?
What are these?
- White and Grey matter.
- Grey matter consists mainly of neuron cell bodies, dendrites, and unmyelinated axons.
- In contrast, white matter consists of bundled axons that have myelin sheaths, which give the axons a whitish appearance.
Where is white matter in the spinal cord and brain, and why?
- White matter in the spinal cord lies on the outside, consistent with its function in linking the CNS to sensory and motor neurons of the PNS.
- White matter in the brain is instead predominantly on the inside, reflecting the role of signaling between neurons of the brain in learning, feeling emotions, processing sensory information, and generating commands.
What is the Spinal cord?
- The spinal cord, which runs lengthwise inside the vertebral column (spine) conveys information to and from the brain and generates basic patterns of locomotion.
- The spinal cord also acts independently of the brain as part of the simple nerve circuits that produce reflexes.
What is the cerebrospinal fluid?
- A fluid hich circulates slowly through the central canal and ventricles and then drains into the veins, supplying different parts of the brain with nutrients and hormones and carrying away wastes.
- In mammals, the cerbrospinal fluid also cushions the brain and the spinal cord by circulating between layers of connective tissue that surround the CNS
What do the dorsal and ventral sides of the spinal cord do?
- Dorsal = Sensory
- Ventral = Motor
What are the 4 functional components of a spinal nerve?
- GSA - General sensory afferent - discriminative touch, pain and temperature from skin, joints, muscles - Somatic
- GVA - General visceral afferent - sensation from the viscera (visceral)
- GVE - General visceral efferent - motor to vicera (viceral)
- GSE - General somatic efferent - motor to skeletal muscles (somatic)
What are 4 special senses?
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