CNS Flashcards
Functions of the nervous system
- Sensory input – gathering information
Sensory Receptors monitor changes, called stimuli - Integration – Processes and interprets sensory input
- Motor output – a response or effect, activates muscles or glands
Organisation of the nervous system
- Structures (structural classification)
2. Activities (functional classification)
Two structural classfications of the nervous system are?
- Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)
Organs and functions of CNS
Organs – Brain and spinal cord
Functions - ▪ Integration; command center
▪ Interprets incoming sensory information
▪ Issues outgoing instructions
Organs and functions of PNS
Nerves extending from the brain and spinal cord
Spinal nerves – carry impulses to and from the spinal cord
Cranial Nerves – Carry impulses to and from the brain
Functions – Serve as communication lines among sensory organs, the brain and spinal cord and glands or muscles
Functional classifications of PNS
- Sensory – sense organs
2. Motor – somatic/voluntary (skeletal muscles) and autonomic/involuntary (cardiac and smooth muscle)
2 principal Nervous tissue cell types
Neurons Supporting cells (Neuroglia)
What are the four types of Glial cells
Astrocytes
Microglial
Ependymal
Oligodendrocytes
Explain features of Astrocytes
- Most abundant and versatile neuroglia
- Positioned between neurons and capillary
- Link nutrient supply in capillaries to neurons and control chemical environment from any harmful substances in the blood.
Explain features of Microglial Cells
Spider like phagocytes that monitor the health of nearby neurons and remove debris like dead bone cells and bacteria
Explain features of Ependymal cells
Line the central cavities of the brain and spinal cord. The cilia maintains cerebrospinal fluid which fills the cavities and forms a watery cushion.
Explain features of Oligodendrocytes cells
▪ Wrap around nerve fibers in the central nervous system
▪ Produce myelin sheaths
Major regions of the Neuron
- Cell body -nucleus and metabolic centre of the cell
- Processes – fibres that extend from the cell body
Components of neuron cell body
▪ Cell body is the metabolic center of the neuron
▪ Nucleus with large nucleolus
▪ Nissl bodies
Rough endoplasmic reticulum
▪ Neurofibrils
Intermediate filaments that maintain cell shape
Components of the neuron processes
Dendrites – conduct impulses toward the cell body (100s)
Axons—conduct impulses away from the cell body ▪ End in axon terminals, which contain vesicles with neurotransmitters
Axon hillock – where axons start
Synaptic cleft—gap between axon terminals and the next neuron
Synapse—functional junction between nerves where a nerve impulse is transmitted
What is Myelin
White, fatty material covering axons ▪ Protects and insulates fibers ▪ Speeds nerve impulse transmission
What is myelin sheaths
Oligodendrocytes—produce myelin sheaths around axons of the CNS ▪ Lack a neurilemma
What are the 3 functional classifications of neurons?
- Sensory Afferent neurons
- Motor efferent neurons
- interneurons
What are the 3 structural classification of neurons and there features?
Multipolar neurons—many extensions from the cell body ▪ All motor and interneurons are multipolar ▪ Most common structural type
Bipolar neurons—one axon and one dendrite ▪ Located in special sense organs, such as nose and eye ▪ Rare in adults
Unipolar neurons—have a short single process leaving the cell body ▪ Sensory neurons found in PNS ganglia ▪ Conduct impulses both toward and away from the cell body
Describe actions of a sensory neuron
▪ Carry impulses from the sensory receptors to the CNS. Cell body is located in ganglion
▪ Receptors include: Dendrites have specific receptors that sense changes nearby ▪ Cutaneous sense organs in skin ▪ Proprioceptors in muscles and tendons
Describe actions of a motor neuron
Carry impulses from the central nervous system to viscera and/or muscles and glands. Cell bodies found within the central nervous system
Describe actions of an Interneurons
Cell bodies located in the CNS ▪ Connect sensory and motor neurons
Action Potential Steps
- The plasma membrane at rest is inactive (polarized- -70 mV). Fewer positive inside than outside. As long as the inside of the membrane is more negative (fewer positive ions) than the outside, the cell remains inactive
- Action potential = nerve impulse. ▪ A graded potential (localized depolarization) exists where the inside of the membrane is more positive and the outside is less positive ▪ If the stimulus is strong enough and sodium influx great enough, local depolarization activates the neuron to conduct an action potential (nerve impulse)
- ▪ If enough sodium enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon ▪ All-or-none response means the nerve impulse either is propagated or is not ▪ Fibers with myelin sheaths conduct nerve impulses more quickly. Reaches 30mV
- ▪ Membrane permeability changes again—becoming impermeable to sodium ions and permeable to potassium ions ▪ Potassium ions rapidly diffuse out of the neuron, repolarizing the membrane ▪ Repolarization involves restoring the inside of the membrane to a negative charge and the outer surface to a positive charge. Less than -70mV. hyperpolerization
- ▪ Initial conditions of sodium and potassium ions are restored using the sodium-potassium pump ▪ This pump, using ATP, restores the original configuration ▪ Three sodium ions are ejected from the cell while two potassium ions are returned to the cell ▪ Until repolarization is complete, a neuron cannot conduct another nerve impulse. Goes back to -70 mV
What is reflex and a reflex arc?
Rapid, predictable and involuntary responses to stimuli
Occur over neural pathways called reflex arcs
2 types of Reflex arcs
Somatic Reflexes
Automatic Reflexes
Explain Somatic Reflexes
All reflexes that stimulate the skeletal muscles
Involuntary, although skeletal muscle is under voluntary control.
E.G. Pulling your hand away from a hot object
Explain Automatic Reflexes
Regulate the activity of smooth muscles, the heart and glands
E.G. Regulation of smooth muscles, heart and blood pressure, glands, digestive system
5 elements of Reflex arc
Sensory receptor – reacts to a stimulus
Sensory neuron – carries message to the integration center
Integration center (CNS) – processes information an directs motor output
Motor neuron – carries messages to an effector
Effector organ – is the muscle or gland to be stimulated
Difference between two-neuron and three neuron reflex arcs
Three neuron arcs are more complicated and has an interneuron
4 main regions of the brain
Cerebral Hemispheres
Diencephalon
Brain Stem
Cerebellum
Explain features of the cerebral hemisphere and the three main regions
Left and right superior parts of the brain
More than half the brain mass
Surface is made of ridges Gyri
Grooves called Sulci
Fissures are deeper grooves
Lobes are named for the cranial bones that lie over them
3 main regions are: 1. Cortex is superficial gray matter (fresh brain tissue) 2. White matter 3. Basal nuclei are deep pockets of gray matter
Cerebral Areas involved in special senses
Visual area (occipital lobe) Auditory Area (temporal lobe) Olfactory area (temporal lobe)
Describe the primary somatic sensory area
▪ Located in parietal lobe posterior to central sulcus
▪ Receives impulses from the body’s sensory receptors
▪ Pain, temperature, light touch (except for special senses)
▪ Sensory homunculus is a spatial map
▪ Left side of the primary somatic sensory area receives impulses from right side (and vice versa)
Describe the primary motor area
▪ Located anterior to the central sulcus in the frontal lobe
▪ Allows us to consciously move skeletal muscles
▪ Motor neurons form pyramidal (corticospinal) tract, which descends to spinal cord
▪ Motor homunculus is a spatial map
What is Broca’s area?
Part of the Cerebral Cortex
▪ Involved in our ability to speak ▪ Usually in left hemisphere
3 Specialized areas of the Cerebral Cortex
▪ Anterior association area (frontal lobe) ▪ Posterior association area (posterior cortex) ▪ Speech area (for sounding out words)
Name of the lobes
Frontal
Parietal
Occipital
Temporal
Describe cerebral white matter
▪ Composed of fiber tracts deep to the gray matter
▪ Corpus callosum connects hemispheres
▪ Tracts, such as the corpus callosum, are known as commissures
▪ Association fiber tracts connect areas within a hemisphere
▪ Projection fiber tracts connect the cerebrum with lower CNS centers
What is basal nuclei
▪ “Islands” of gray matter buried deep within the white matter of the cerebrum ▪ Regulate voluntary motor activities by modifying instructions sent to skeletal muscles by the primary motor cortex
What is the diencephalon and components of it?
▪ Sits on top of the brain stem
▪ Enclosed by the cerebral hemispheres
▪ Made of three structures 1. Thalamus 2. Hypothalamus 3. Epithalamus
What is the thalamus
▪ Encloses the third ventricle ▪ Relay station for sensory impulses passing upward to the cerebral cortex ▪ Transfers impulses to the correct part of the cortex for localization and interpretation
What is the hypothalamus
▪ Makes up the floor of the diencephalon
▪ Important autonomic nervous system center ▪ Regulates body temperature ▪ Regulates water balance ▪ Regulates metabolism
▪ Houses the limbic center for emotions
▪ Regulates the nearby pituitary gland
▪ Houses mammillary bodies for olfaction (smell)
What is the epithalamus
▪ Forms the roof of the third ventricle
▪ Houses the pineal body (an endocrine gland)
▪ Includes the choroid plexus—forms cerebrospinal fluid
What is the brain stem
▪ Attaches to the spinal cord
▪ Parts of the brain stem
1. Midbrain 2. Pons 3. Medulla oblongata
Describe the midbrain
▪ Extends from the mammillary bodies to the pons inferiorly
▪ Cerebral aqueduct (tiny canal) connects the third and fourth ventricles
▪ Two bulging fiber tracts, cerebral peduncles, convey ascending and descending impulses
▪ Four rounded protrusions, corpora quadrigemina, are visual and auditory reflex centers
Describe pons
▪ The rounded structure protruding just below the midbrain ▪ Mostly composed of fiber tracts ▪ Includes nuclei involved in the control of breathing
Describe medulla oblongata
▪ The most inferior part of the brain stem that merges into the spinal cord ▪ Includes important fiber tracts
▪ Contains important centers that control: ▪ Heart rate ▪ Blood pressure ▪ Breathing ▪ Swallowing ▪ Vomiting
What is reticular formation
▪ Diffuse mass of gray matter along the brain stem ▪ Involved in motor control of visceral organs ▪ Reticular activating system (RAS) ▪ Plays a role in awake/sleep cycles and consciousness ▪ Filter for incoming sensory information
What is the cerebellum
2 hemispheres with convulated surface
Outer cortex of gray matter and inner region of white matter
Controls balance
Provides precise timing for skeletal muscle activity and coordination of body movements
Fibres reach the cerebellum from the equilibrium apparatus from the inner ear, the eye and skeletal muscles.
Sends messages to body for smooth and coordinated actions
Movement becomes disorganised and clumsy if this part is damaged
Protection of the CNS
▪ Meninges ▪ Cerebrospinal fluid (CSF) ▪ Blood-brain barrier
Components of the Meninges
Dura mater
Arachnoid Space
Pia mater
Explain the Cerebrospinal fluid
▪ Similar to blood plasma in composition
▪ Formed continually by the choroid plexuses
▪ Choroid plexuses—capillaries in the ventricles of the brain
▪ CSF forms a watery cushion to protect the brain and spinal cord
▪ Circulated in the arachnoid space, ventricles, and central canal of the spinal cord
Steps of the cerebrospinal fluid circulation
- CSF is produced by the choroid plexus of each ventricle
- CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord
- CSF flows through the subarachnoid space
- CSF is absorbed into the dural venous sinuses via the arachnoid villi
Features of the blood brain Barrier
▪ Includes the least permeable capillaries of the body
▪ Allows water, glucose, and amino acids to pass through the capillary walls
▪ Excludes many potentially harmful substances from entering the brain, such as wastes
▪ Useless as a barrier against some substances (fats, respiratory gases). Blood born alcohol, nicotine impact brain.
Name 5 traumatic brain injuries
- Concussion – Slight brain injury, little perm. Damage
- Contusion – marked nervous tissue destruction occurs, coma may occur
- Death may occur due to head blows: Intracranial haemorrhage, Cerebral Edema
- Cerebrovascular accident (CVA) or stroke
▪ Results when blood circulation to a brain area is blocked and brain tissue dies
▪ Loss of some functions or death may result ▪ Hemiplegia—one-sided paralysis ▪ Aphasia—damage to speech center in left hemisphere - Transient Ischemic Attack (TIA)
▪ Temporary brain ischemia (restriction of blood flow) ▪ Numbness, temporary paralysis, impaired speech
May be warning for a more serious issue
How many pairs of spinal nerves come from spinal cord
31, provide two way conduction pathway to brain
Grey matter of spinal cord
▪ Internal gray matter is mostly cell bodies
▪ Dorsal (posterior) horns house interneurons
▪ Receive information from sensory neurons in the dorsal root; cell bodies housed in dorsal root ganglion
▪ Anterior (ventral) horns house motor neurons of the somatic (voluntary) nervous system
▪ Send information out ventral root ▪ Gray matter surrounds the central canal, which is filled with cerebrospinal fluid
White matter of spinal cord
▪ Composed of myelinated fiber tracts
▪ Three regions: dorsal (ascending), lateral (ascending and descending), ventral columns (ascending and descendimg) ▪ Sensory (afferent) ascending tracts conduct impulses toward brain
▪ Motor (efferent) descending tracts carry impulses from brain to skeletal muscles
Describe the Dura Matter
▪ Outermost leathery layer
▪ Double-layered external covering ▪ Periosteum—attached to inner surface of the skull ▪ Meningeal layer—outer covering of the brain
▪ Folds inward in several areas ▪ Falx cerebri ▪ Tentorium cerebelli
Describe the Pia Matter
Internal layer ▪ Clings to the surface of the brain and spinal cord
Describe the Arachnoid Layer
▪ Middle layer ▪ Weblike extensions span the subarachnoid space to attach it to the pia mater ▪ Subarachnoid space is filled with cerebrospinal fluid ▪ Arachnoid granulations protrude through the dura mater and absorb cerebrospinal fluid into venous blood
What are some receptors?
- Free nerve endings (pain and temperature receptors)
- Meissner’s corpuscle (touch receptor)
- Lamellar Corpuscle (Deep pressure receptor)
- Golgi tendon organ and muscle spindle (proprioceptor)
