Nervous System: Tissue Flashcards
1
Q
What is nervous tissue made of?
A
- Neurons and glial cells
2
Q
What is the CNS?
A
- Includes the brain and spinal cord
- The brain is protected and enclosed by the skull
- The spinal cord is protected and enclosed within the vertebral canal
3
Q
What is the PNS?
A
- Includes cranial nerves (extend from brain), spinal nerves (extend from spinal cord), and ganglia (clusters of neuron cell bodies located out of the CNS)
4
Q
What do sensory and motor divisions of the nervous system do?
A
- Collect information through PNS receptors
- Process and evaluate information in which CNS determines if any response is required
- Initiate response to information by CNS producing motor output to effectors
5
Q
What are PNS receptors?
A
- Collect information
- The dendrite endings of sensory neurons or separate cells
- Detect changes in internal or external environment (stimuli) and pass them on to the CNS sensory input
6
Q
What is CNS motor output?
A
- After selecting an appropriate response, CNS initiates specific nerve impulses
- They are rapid movements of an electrical charge along the neuron’s plasma membrane of an axon
- Travels through structures of the PNS to effectors
7
Q
What is the sensory nervous system?
A
- Or afferent nervous system
- Responsible for receiving sensory information from receptors and transmitting this information to the CNS
- Responsible for sensory input
- Contains both PNS and CNS components
- PNS nerves: transmit sensory information
- CNS nerves: in brain and spinal cord interpret the information
- Has 2 components: somatic sensory and visceral sensory
8
Q
What are the somatic sensory components?
A
- General somatic senses: touch, pain, pressure, vibration, temperature and proprioception (sensing position or movement of joints and limbs)
- Also special senses: taste, vision, hearing, balance and smell
- These functions are considered voluntary because we have some control over them and we tend to be conscious of them
9
Q
What are the visceral sensory components?
A
- Transmit nerve impulses from blood vessels and viscera to the CNS
- Visceral receptors detect chemical composition of blood or stretch an organ wall
- These functions are considered involuntary because most of the time you don’t have voluntary control over them and are not conscious of them
- You may become aware of visceral sensations when they are extreme (eaten too much and your stomach is bloated)
10
Q
What is the motor nervous system?
A
- Also known as efferent; conducting outward
- Responsible for transmitting motor impulses from the CNS to effectors (muscles or glands)
- Responsible for output of nerve impulses, transmitted from CNS
- Has CNS and PNS components
- Divided into somatic motor and autonomic motor components
11
Q
What is the somatic motor component?
A
- Conducts nerve impulses from the CNS to the skeletal muscles, causing them to contract
- Is the voluntary nervous system, because the contractions of the skeletal muscles are under conscious control
12
Q
What is the autonomic motor component?
A
- Is the autonomic nervous system, because it innervates internal organs and regulates smooth muscle, cardiac muscle and glands without our control
- Also known as the visceral motor system or involuntary nervous system
13
Q
What are neurons?
A
- The basic structural unit of the nervous system
- Neurons conduct nerve impulses from one part of the body to another
- The have: high metabolic rates, extreme longevity, nonmitotic (unable to divide and produce new neurons), excitable and conductive
14
Q
What is the cell body? (neuron)
A
- Also called a soma
- Serves as the neurons control center and is responsible for receiving, integrating and sending nerve impulses
- Inclosed by a plasma membrane and contains cytoplasm surrounding the nucleus
15
Q
What is the nucleolus? (neuron)
A
- Within the nucleus
- Reflects the high metabolic activity of neurons, which require the production of many proteins
16
Q
WHat do the mitochondria do? (neuron)
A
- Numerous are present within the cytoplasm to produce large amounts of ATP needed by the neuron
17
Q
What is chromatophilic substance? (neuron)
A
- Both free and bound ribosomes
- Together, with dendrites and cell bodies, account for the gray colour of gray matter
18
Q
What are dendrites? (neuron)
A
- Tend to be shorter, smaller processes that branch off the cell body
- Some neurons have only one dendrite , whereas others have many
- Conduct information as electrical signals from other cells toward the cell body
- Receive input and transfer it to the cell body for processing
- The more dendrites a neuron has, the more info that neuron can receive from other cells
- Some dendrite surface areas are increased by small knoblike protuberances called dendritic spines
- The more surface area a neuron has, the more interactions it will have with other cells
19
Q
What is the axon? (neuron)
A
- Typically a longer nerve cell process emanating from the cell body to make contact with other neurons, muscle cells or gland cells
- Neurons either have one, or none at all
- Neurons without axons are called anaxonic (found in CNS as interneurons)
- Transmits nerve impulses away from the cell body, transmitting output info to other cells
20
Q
What is the axon hillock? (neuron)
A
- Triangular region of the cell body
- Where the axon extends from
- A devoid of chromatophilic substance
21
Q
What is a axon collateral? (neuron)
A
- Side branches of the axon
- Branch extensively at the distal end into an array of fine terminal extensions called terminal arborizations
- The tips of terminal arborizations have expanded regions called synaptic knobs
22
Q
What is perikaryon? (neuron)
A
- Cytoplasm within the cell body
23
Q
What are neurofibrils? (neuron)
A
- The aggregation of neurofilaments (form bundles)
- Extend as a complex network into both the dendrites and axons, where their tensile strength provides support for those processes
- Can be described as neuron structures
24
Q
What are unipolar neurons?
A
- Have a single, short process that emerges from the cell body and branches like a ‘T’
- Start out as bipolar neurons during development, but their 2 processes fuse into one
- The combined peripheral process and central process denote the axon because they generate and conduct impulses and are myelinated
- Most sensory neurons of the PNS are unipolar
25
Q
What are bipolar neurons?
A
- Have 2 processes that extend from the cell body: one axon and one dendrite
- These tend to be uncommon in humans and primarily limited to some of the special senses
- Located in the olfactory epithelium of the nose and retina of the eye for examples
26
Q
What are multipolar neurons?
A
- The most common type of neuron
- Have multiple processes, many dendrites and a single axon
- Examples include motor neurons that innervate muscle and glands
27
Q
What are sensory neurons?
A
- Also known as afferent neurons
- Transmit nerve impulses from sensory receptors to the CNS
- Specialized to detect changes in their environment called stimuli (touch, pressure, heat, light or chemicals)
- Most are unipolar although a few are bipolar
- The cell bodies of unipolar sensory neurons are located outside of the CNS and housed in posterior root ganglia
28
Q
What are motor neurons?
A
- Also known as efferent neurons
- Transmit nerve impulses from the CNS to muscles and glands
- Most extend to muscle cells and nerve impulses they transmit cause those cells to contract
- The muscle and gland cells that receive nerve impulses from motor neurons are called effectors (their stimulation produces a response or effect)
- The cell bodies of most motor neurons lie in the spinal cord, whereas their axons primarily travel in cranial or spinal nerves to muscles and glands
- All motor neurons are multipolar
29
Q
What are interneurons?
A
- Also known as association neurons
- Lie entirely within the CNS and are multipolar structures
- Receive nerve impulses from many other neurons and carry out that integrative function of the nervous system
- They retrieve, process and store information and decide how the body responds to stimuli
- Facilitate communication between sensory and motor neurons
- It is estimated that 99% of our neurons are interneurons
- The number of interneurons involved during processing and story information, increases dramatically with the complexity of the response
30
Q
What are glial cells?
A
- Sometimes referred to as neuroglia
- Located within both the CNS and PNS
- Differ from neurons in that they are smaller and capable of mitosis
- Do not transmit nerve impulses, but do assist neurons with their functions
- They physically protect and help nourish neurons and provide an organized, supporting framework for all nervous tissue
- During development, glial cells form the framework that guides young migrating neurons to their destinations
- Also play a role in learning and memory through their interaction with synapses between neurons
- Collectively, glial cells account for roughly half the volume of the nervous system
31
Q
What are the glial cells of the CNS?
A
- 4 types: astrocytes, ependymal cells, microglial cells and oligodendrocytes
- Can be distinguished by the basis of size, intercellular organization and the presence of specific cytoplasmic processes
- All glial cells except for microglia are derived from neural ectoderm
- Microglia are derived from stem cells within red bone marrow that become monocytes (a type of white blood cell)
32
Q
What are astrocytes? (CNS glial)
A
- Exhibit a starlike shape due to many projections from their surface
- The numerous cell processes touch both capillary walls and different parts of neurons
- Most abundant glial cell in the CNS and constitute over 90% of the nervous tissue in some areas of the brain
- Subpopulations are fibrous and protoplasmic astrocytes
- Help form the blood-brain barrier (perivascular feet wrap around and cover the outer surface of the brain capillaries)
- Regulate tissue fluid composition
- Replace damaged neurons
- Assist neural development
- Help regulate synaptic transmission (2 way communication between astrocytes and neurons at the synapse)
- Change synapse numbers
33
Q
What is the blood-brain barrier? (astrocyte)
A
- Strictly controls substances entering the nervous tissue in the brain from the blood
- Protects the delicate brain from toxins
- Allows needed nutrients to pass through
- Sometimes it is detrimental when some meds cannot exit capillaries and enter the nervous tissue of the brain
34
Q
What are ependymal cells? (CNS glial)
A
- Cuboidal epithelial cells that line the internal cavities of the brain and the central canal of the spinal cord
- Have slender processes that branch extensively to make contact with other glial cells in the surrounding tissue
- These cells and blood capillaries together form a network called the choroid plexus, which produces cerebrospinal fluid that bathes the CNS and fills its cavity
- Ependymal cells have cilia on their apical surfaces that help circulate the fluid
35
Q
What are microglial cells? (CNS glial)
A
- Represent the smallest percentage of CNS glial cells
- Typically small cells that have slender branches extending from the main cell body
- Wander through the CNS and replicate in response to infection
- Perform phagocytic activity and remove debris from dead or damaged nervous tissue (janitors)
36
Q
What are oligodendrocytes? (CNS glial)
A
- Large cells with a bulbous body and slender cytoplasmic processes
- Their processes ensheath portions of many different axons, each repeatedly wrapping around part of an axon like electrical tape around a wire (myelin sheath)
- Can myelinate 1 mm length portion of many axons, not just one
- The cells successive plasma membrane layers form the myelin sheath
37
Q
What are satellite cells? (PNS glial)
A
- Flattened cells arranged around neuronal cell bodies in ganglia
- Physically separate cell bodies in ganglion from their surrounding interstitial fluid
- Regulate the continuous exchange of nutrients and waste products between neurons and their environment
38
Q
What are neurolemmocytes? (PNS glial)
A
- Also called schwann cells
- Associated with PNS axons
- Are elongated, flattened cells that wrap around the axons of the PNS, insulating the axon and forming a myelin sheath
- Neurilemma is used to describe the delicate, thin, outer membrane of the neurolemmocyte
- The overlapping inner layers of plasma membrane form the myelin sheath in these cells
- These cells can only myelinate 1 mm length portion of a single axon only
39
Q
What is myelin sheath/myelination?
A
- The process by which part of an axon is wrapped with a myelin sheath, the insulating covering around the axon consisting of concentric fibers of myelin
- CNS: formed by oligodendrocytes
- PNS: formed by neurolemmocytes
- Myelin consists of the plasma membranes of these glial cells and contain a large proportion of fats and a lesser amount of proteins
- The high lipid content of myelin sheath gives the axon a distinct, glossy, white appearance and serves to effectively insulate it
40
Q
What are unmyelinated axons?
A
- PNS: associated with a neurolemmocyte, but no myelin sheath covers them
- CNS: not associated with oligodendrocytes
41
Q
What are neurofibril nodes?
A
- Small spaces that interrupt the myelin sheath on the axon
- These nodes can change the voltage across the plasma membrane and result in the movement of a nerve impulse
- Nerve impulses seem to “jump” from node to node along the axon (saltatory conduction) and this only occurs in myelinated axons
- In unmyelinated axons, continuous conduction occurs across the whole axon
42
Q
Why do myelinated axons produce a faster nerve impulse?
A
- Only the exposed membrane regions are affected as the impulse moves toward the end of the axon (this is rapid and sends the impulse quickly to skeletal muscles and limbs)
- In an unmyelinated axon, the nerve impulse takes longer because every part of the membrane must be affected by the voltage change (conduct nerve impulses from pain and some cold stimuli)
43
Q
What is PNS axon regeneration?
A
- These axons are vulnerable to cuts, crashing injuries and other types of trauma
- A damaged axon can regenerate if the cell body remains intact and a critical amount of neurilemma remains
- Its success of regenerating depends on: amount of damage and the distance between the site of the damaged axon and the structure it innervates
44
Q
What are nerves?
A
- Cable like bundles of parallel axons
- Has 3 successive connective tissue wrappings: endoneurium, perineurium and epineurium
- Components of the peripheral nervous system
45
Q
What is endoneurium? (nerve)
A
- An individual axon in a myelinated neuron is surrounded by neurolemmocytes and then wrapped in endoneurium
- A delicate layer of areolar connective tissue that separates and electrically isolates each axon
- Within this connective tissue layer are capillaries that supply each axon
46
Q
What is perineurium? (nerve)
A
- Groups of axons are wrapped into separate bundles called fascicles by a cellular dense irregular connective tissue layer caller perineurium
- This layer supports blood vessels supplying capillaries within the endoneurium
47
Q
What is epineurium? (nerve)
A
- All of the fascicles are bundled together by a superficial connective tissue covering called epineurium
- This thick layer of dense irregular connective tissue encloses the entire nerve
- Provides both support and protection to the fascicles within the layer
48
Q
What are synapses?
A
- Axons terminate as they contact other neurons, muscle cells or gland cells at specialized junctions called synapses, where the nerve impulse is transmitted to the other cell
- As the axon approaches the cell onto which it will terminate, it generally branches repeatedly into several unmyelinated terminal arborizations
- The synaptic endings normally have swellings called synaptic knobs at the end of each axon branch
- A typical synapse in the CNS consists of the association between a presynaptic and postsynaptic neuron at a space where their plasma membranes are separated by a space called the synaptic cleft
- 3 common types: axodendritic, axosomatic, axoaxonic
49
Q
What are presynaptic/postsynaptic neurons?
A
- Pre: transmit nerve impulses through their axons towards a synapse
- Post: conduct nerve impulses through their dendrites and cell bodies away from the synapse
