Lecture 11: Nervous Tissue Flashcards
What are the functions of the nervous system
- Sensory input
- information gathered by sensory receptors about interval and external changes - Integration: interpretation of sensory input
- Motor output: activation of effector organs (muscles and glands) produces a response
- or activation of another neuron
What are the two divisions of the nervous system, what are their functions?
- Central nervous system: brain and spinal cord, it’s the integration and command centre
- Peripheral nervous system (PNS): paired spinal and cranial nerves carry messages to and from the CNS
What are the two functional divisions of the PNS
- Sensory (afferent) division
- somatic afferent fibres- convey impulses from skin, skeletal muscles, and joints
- visceral afferent fibres- convey impulses from visceral organs - Motor (efferent) division:
- transmits impulses from the CNS to effector organs
What are the motor divisions of the PNS?
- Somatic (voluntary) nervous system
-conscious control of skeletal muscles - Autonomic (involuntary) nervous system (ANS)
-visceral motor nerve fibres
-regulates smooth muscle, cardiac muscle, and glands
-two functional subdivisions
Sympathetic and parasympathetic
What are the two types of nervous tissue
- Neurons- excitable cells that transmit electrical signals
-long lived 100 yrs or more
-high metabolic rate- needs lots of o2 and glucose - Neuroglia (glial cells)- supporting cells
A) astrocytes CNS: most abundant and highly branched glial cells, cling to neurons, synaptic endings, and capillaries
-support and brace neurons
-control the chemical permeability
B) microglia CNS (defensive cells)
-small thorny processes which migrate towards injured neurons
-phagocytize microorganisms and neural debris
C) ependymal cells CNS
-line the central cavities of the brain and spinal column
-job is to separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities
D) oligodendrocytes CNS
-have processes that form myelin sheath around CNS nerve fibres
E) schwann cells PNS
Define neuron, describe its important structural components, and relate each to a functional role.
Cell body: spherical nucleus with nucleolus
-well developed Golgi apparatus
-rough endoplasmic reticulum called Nissl bodies
-network of neurofibrils (neurofilaments)
-clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS
Processes:
Dendrites:
-receptive input region of neuron, convey electrical signals toward the cell body as graded potentials
Axons:
-knoblike axon terminals (synaptic knobs or boutons) which is the secretory region of a neuron, which releases neurotransmitters to excite or inhibit other cells
Explain the importance of myelin sheath and describe how it is formed in the central and peripheral nervous system
Myelin sheath is segmented protein-lipid sheath around most long or large diameter axons. It functions to:
- protect and electrically insulate the axon
- increase speed of nerve impulse transmission
Myelin sheath in the PNS
Schwann cells: wraps many times around the axon
Neurilemma: peripheral bulge of Schwann cell cytoplasm
Nodes of ranvier: myelin sheath gaps between adjacent Schwann cells
Myelin sheaths in the CNS:
- formed by processes of oligodendrocytes, not the whole cells
- nodes of ranvier are present
- no neurilemma
- thinnest fibres are unmyelinated
What is the difference between grey matter and white matter
White matter: dense collections of myelinated fibres
Gray matter: mostly neurons cell bodies and unmyelinated fibres
What are the three different structures of neurons
- Multipolar: 1 axon and several dendrites
- most abundant
- motor neurons and interneurons - Bipolar: 1 axon and 1 dendrite
- rare eg retinal neurons - Unipolar: single, short process that has two branches:
- peripheral process which is a more distal branch coming from a sensory receptor
- then a central process-which is a branch entering the CNS
- found mainly in the PNS
What are the three types of neurons?
- Sensory (afferent): transmits impulses from sensory receptors towards the CNS
- Motor (efferent): carry impulses from the CNS to the effectors
- Interneurons (association neurons): shuttle signals through CNS pathways; most are entirely within the CNS
What are the three nerve fibre classifications:
Group A fibres: large diameter, myelinated somatic sensory and motor fibre
Group B: intermediate diameter, lightly myelinated ANS fibres
Group C: smallest diameter, unmyelinated ANS fibres
What is a synapse, and what happens here?
A junction that mediates the transfer from one neuron:
- to another neuron or
- to an effector cell: muscle or gland
