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Lecture 1

ANAT 1010 Lecture Notes - Lecture 1: Central Nervous System, Nervous Tissue, Spinal CordPremium

11 pages15 viewsFall 2018

Department
Anatomy
Course Code
ANAT 1010
Professor
A. Jaffar
Lecture
1

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Lecture 1: Nervous Tissue
October 5, 2018
Nervous Tissue:
- Controls and integrates all body activities (along with the endocrine system)
- Three basic functions:
a. Sensory sensing changes with sensory receptors
b. Integration interpreting and remembering those changes
c. Motor reacting to those changes with effectors (muscular contractions;
glandular secretions)
The nervous system is one of the smallest and yet the most complex of the 11 body systems.
It is a highly organized network of 2 cell types contains billions of neurons and more
neuroglia. The structures that compose the nervous system include: the brain, cranial nerves
and their branches, the spinal cord, spinal nerves and their branches, ganglia, enteric plexuses,
and sensory receptors.
The nervous system’s activities can be grouped into 3 basic functions:
1. Sensory function:
o Sensory/afferent neurons carry sensory information (internal stimuli + external
stimuli) into the brain/spinal cord through cranial + spinal nerves.
2. Integrative Function:
o Nervous system processes sensory information by analyzing and storing some of
the information and making decisions for appropriate responses.
o Includes perception (conscious awareness of sensory stimuli occurs in brain).
o Interneurons (neurons that interconnect with other neurons) with axons that
extend for a short distance will contact nearby neurons and in the brain/spinal
cord to set up the circuit boards of the CNS. majority of neurons in CNS.
3. Motor Function:
o Once sensory information is integrated, the nervous system may elicit an
appropriate motor response (i.e. muscular contraction/glandular secretion)
o The neurons that serve this function are referred to as “motor/efferent
neurons”
o Carries information from the brain towards the spinal cord, or out of the brain +
spinal cord towards “effectors” (muscles/glands) through cranial and spinal
nerves.
o The stimulation of the effectors by motor neurons causes the muscles to
contract and glands to secrete.
Divisions of the Nervous System:
1. Central Nervous System (CNS): “brain and spinal cord”
o The brain is enclosed and protected by the skull in cranial cavity and contains ~
85 billion neurons.
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o Spinal cord is enclosed and protected by the bones of the vertebral column in
the vertebral canal and contains ~ 100 million neurons.
o CNS processes many different kinds of incoming sensory information and is the
source of thoughts, emotions, and memories.
o Most nerve impulses that stimulate muscles to contract and glands to secrete,
originate in the CNS.
2. Peripheral Nervous System (PNS): “cranial and spinal nerves containing sensory/motor
fibers”
o All nervous structures that are outside of the CNS (i.e. cranial nerves + branches;
spinal nerves + all of their branches; sensory receptors).
o These structures link all of the parts of the body to the CNS (muscles, glands,
and all sensory receptors).
Divisions of the PNS:
1. Somatic (voluntary):
- Consists of sensory neurons (somatic sensory neurons) that convey information to the
CNS from the sensory receptors in the skin, skeletal muscles, and joints, and from the
receptors for the special senses (i.e. vision, hearing, equilibrium, taste, and smell.)
- Also consists of somatic motor neurons, that convey information from the CNS to the
skeletal muscles only. “somatic motor pathways” – involved in the CNS’s output of
information that results in muscular contraction.
- The motor responses can be CONSCIOUSLY CONTROLLED thus, the actions of these
parts of the SNS are “voluntary”.
2. Autonomic (involuntary):
- Also has sensory and motor components.
- Sensory neurons (autonomic (visceral) sensory neurons) convey information to the
CNS from autonomic sensory receptors, primarily in the visceral organs (i.e. smooth
muscle organs in the thorax, abdomen, and pelvis).
- Autonomic motor neurons will convey information from the CNS to the smooth
muscle, cardiac muscle, and glands and cause the muscles to contract and the glands
to secrete.
- Motor responses are NOT normally under conscious control the action of ANS is
involuntary.
- 3 subdivisions of the ANS (2 main + 1 small subdivision)
a. Sympathetic division: “fight or flight”
b. Parasympathetic division: “rest and digest”
c. Enteric nervous system: “local circuit neurons in the gut” sensory neurons of the
ENS will monitor chemical changes within the GI tract, as well as the stretching of
its walls; motor neurons of the ENS govern the contraction of the GI tract smooth
muscle to propel food through the GI tract + control secretions of the GI tract
organs (i.e. stomach acid) and endocrine cells (secrete hormones).
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Histology of Nervous Tissue:
Nervous tissue is comprised of 2 cell types neurons and neuroglia (“nerve glue”), that
combine in a variety of ways in different regions of the nervous system.
In addition to forming complex processing networks within the brain and spinal cord, neurons
comprise the circuitry that connects all body regions to this central processing unit. As highly
specialized cells that are capable of reaching great lengths and making extremely intricate
connections with other cells, the neurons provide most of the unique functions of the NS (i.e.
sensing, thinking, remembering, controlling muscle activity and regulating glandular secretions).
Neuroglial Cells:
- Half of the volume of CNS
- Smaller cells than neurons
- 50x more numerous
- Cells can divide: rapid mitosis in tumor formation (gliomas)
- 4 cell types in CNS (astrocytes, oligodendrocytes, microglia, and ependymal)
- 2 cell types in PNS (Schwann and satellite cells)
Neuroglia cells are smaller but outnumber neurons. They support, nourish, and protect
neurons, and maintain the interstitial fluid that bathes them.
Unlike neurons, the neuroglia cells continue to divide throughout the lifetime of an individual,
and the structures of both neurons + neuroglia will differ depending on whether they are
located in the CNS and the PNS. The differences in structure correlates with differences in the
function in these 2 branches of the NS.
Astrocytes:
- Star shaped cells
- Form blood-brain barrier by covering blood capillaries
- Metabolize neurotransmitters
- Regulate potassium ion balance
- Provide structural support
The largest and most numerous neuroglia cell, they are star-shaped cells that have many arm-
like processes.
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