Chapter 11 : organization of nervous tissue Flashcards
Homeostasis
= maintenance of stable internal environment within healthy range despite changes that occur in external environment
• maintains temp, pH, glucose levels, calcium levels, osmolarity, blood pressure…..
• maintains protein conformation and optimal enzyme function
• All of the cells in the human body must work together to maintain homeostasis.
• Ex : Heart cells must contract at a rate that ensures adequate delivery of blood to all tissues of the body.
• The nervous sys can stimulate or inhibit these activities to help maintain homeostasis.
What are the 2 major control systems ?
And what are their function ?
1)nervous and endocrine
2) - maintain homeostasis
o alter body function to meet changing conditions
o controller ?
either central nervous system (CNS) or endocrine gland
• responds to receptor signal
• sends message to effectors to return toward homeostasis
o effectors ?
- muscles, glands, specialized cells
• respond to signals from controller and corrects imbalances or adjusts body function to meet current needs
Nervous system?
o detect change and send signals via nerves
o fast response, short term regulation
- brain, spinal cord, nerves and sensory receptors
o protected by bone: brain within skull, spinal cord within vertebral column
Endocrine system ?
o send signals via hormones
o slower response, long term regulation
what are the 2 feedback patterns of responses to signals from receptors ?
1) negative feedback
2) positive feeback
Negative feedback ?
most commonly used mechanism
o sensors detect difference from set‐point: controllers stimulate effectors to return to normal
o ex : When blood sugar rises, receptors in the body sense a change . In turn, the control center (pancreas) secretes insulin into the blood effectively lowering blood sugar levels. Once blood sugar levels reach homeostasis, the pancreas stops releasing insulin.
o Hence, the output decreases the original effect of the stimulus.
Positive feedback ?
sensors detect difference from set‐point( from homeostasis) : controllers move the system farther from the set point
• A good example of a positive feedback system is child birth. During labor, a hormone called oxytocin is released that intensifies and speeds up contractions. The increase in contractions causes more oxytocin to be released and the cycle goes on until the baby is born. The birth ends the release of oxytocin and ends the positive feedback mechanism.
• Hence, + feedback is when the output increases the original stimulus.
grey matter ?
location of nerve cell bodies and their dendrites with very little myelin and sites of synaptic connections between neurons
cortex ?
grey matter covering the surface of the brain
nuclei ?
islands of grey matter deep within the brain
nerve tracts ?
= white matter
ascending and descending bundles of parallel axons and their myelin sheaths (whitish in color) within the CNS
Peripheral nervous sys
all nervous tissue outside CNS
o sensory receptors
ends of neurons that are specialized to detect various internal or external stimuli and transduce (convert) them into electrical impulses
There’s two types:
1) general sensory receptors
2) special sensory receptors
• general sensory receptors
have wide distribution in skin, muscle, joints and organs and detect pain, temperature, touch, pressure, body position, and blood composition and osmolarity
• special sensory receptors
located within special sensory organs in the head and responsible for taste, smell, hearing, vision, and equilibrium
nerves
bundles of nerve fibers (axons) and their myelin sheaths = white matter
• enter and leave CNS. It connects the CNS to sensory receptors, muscles and glands.
How many pairs of cranial nerves does the brain has ?
12 pairs
how many pairs of spinal nerves does the spinal cord has ?
31 pairs
plexus
extensive network of axons in PNS
ganglion ?
o = cluster of nerve cell bodies in PNS
afferent divison
The nerves responsible for sensing a stimulus and sending information about the stimulus to your central nervous system
Think “towards”
Another definition : transmit electrical impulses (action potentials) from sensory receptors into the CNS.
• enter CNS via dorsal root of spinal cord
ex : if you felt scorching heat on your hand, the message would travel through afferent pathways to your central nervous system.
efferent division
Think of “away”
– transmit action potentials from CNS to effectors
another definition :
- The nerves that carry signals away from the central nervous system in order to initiate an action
• Continuous of previous ex: It would then interact with the effector and travel down the efferent pathway, eventually making the person remove their hand from the scorching heat.
The motor division is divided into 2 subdivisions :
1) somatic nervous system
– voluntary (consciously control movement of our skeletal muscles) division that supplies skeletal muscle
o cell body located in CNS and axons extend out via nerves to skeletal muscle
o Action potential originates in CNS and are transmitted by the somatic nervous sys to the same skeletal muscles.
2) autonomic nervous system
– involuntary (Controls unconscious activities) division that supplies contractions of cardiac muscle, smooth muscle and glands
Autonomic nervous sys is divided into 2 divisions :
1) sympathetic nervous division (SNS) – most active during physical activity
2) parasympathetic nervous division (PNS)
– regulates activities that occur at rest ex : digesting food or emptying the urinary bladder.
neurons ?
receive stimuli, conduct action potentials and transmit signals to other neurons or effector organs and neuroglia
neuroglia ?
support cells
it support and protect neurons.
myelinated axons
multi-layered phospholipid covering form by extensions of oligodendrocytes that wrap around axons in CNS and Schwann cells in PNS
multipolar neurons
dominant type of neuron, most of the neurons within the CNS and motor neurons – has multiple processes extending from cell body. Have many dendrites and one axon.
bipolar
found in special sense organs (eye, ear) – have two process extending from cell body : one dendrite and one axon.
pseudo-unipolar neuron
primary sensory neurons that have cell bodies in dorsal root ganglion
– appear to have only one process This process divides into two branches, one branch extends to the CNS, and the other extend extends to the periphery and has dendrite like sensory receptors.
Check image.
Astrocytes (type of neuroglial cells)
– help regulate extracellular composition of cerebral spinal (=brain) fluid
o They do it by releasing chemicals that promote the formation of tight junctions bet the endothelial (look it up) cells of capillaries.
o extensions widen and spread out to form foot processes , which cover the surface of the blood vessels, neurons and the pia matter ( is a membrane covering the outside of the brain and spinal cord) .
• extensions contact surfaces on capillaries at blood-brain barrier (tight junctions between endothelial cells of blood vessels that limits passage of substances in blood to cerebral spinal fluid) in other words, det. What substances can pass from the blood into the nervous tissue of the brain and spinal cord.
• It helps protects neurons from toxic substances in the blood and prevents fluctuations in blood composition from affecting brain functions.
• help limit spread of inflammation to the surrounding healthy tissue and damage to CNS but also form scar tissue that limits regeneration of axons of injured neurons
ependymal cells (type of neuroglial cells)
line ventricles of brain and central canal of spinal cord and cilia help circulate cerebral spinal fluid
o microglia (type of neuroglial cells)
phagocytes of CNS becomes mobile and phagocytic in response to inflammation. Moves in response to damage by infection, trauma or stroke and perform phagocytosis.
oligodendrocytes (type of neuroglial cells)
extensions from each cell wraps around numerous axons in CNS forming myelin sheaths if it warps around the axons multiple times.
Schwann cells
– in PNS - individual cells each wrap around a single axon forming a myelin sheath
satellite cells
in PNS - provide support, nutrition and protection to neuron cell bodies in ganglions
