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Nervous System Notes
Nursing (RLE70)
Capitol University
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Nervous System Functions
Receiving sensory input
Integrating information
Controlling muscles and glands
Maintaining homeostasis
Establishing and maintaining mental activity
Main Divisions of Nervous System 1
‐ Central nervous system (CNS)
‐ brain and spinal cord
‐ Peripheral nervous system (PNS)
‐ All the nervous tissue outside the CNS
‐ Sensory division (afferent)
‐ Conducts action potentials from sensory receptors to the CNS
‐ Motor division (efferent)
‐ Conducts action potentials to effector organs such as muscles and glands
Somatic nervous system
‐ Transmits action potentials from the CNS to skeletal muscles.
‐ Autonomic nervous system
‐ Transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands
‐ Enteric nervous system
‐ A special nervous system found only in the digestive tract.
Cells of the Nervous System
‐ Neurons
‐ receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs.
‐ Glial cells (neuroglia)
‐ supportive cells of the CNS and PNS, meaning these cells do not conduct action potentials. Instead, glial cells carry out different functions that enhance neuron function and maintain normal conditions within nervous tissue.
Neurons
‐ A neuron (nerve cell) has a:
‐ Cell body – which contains a single nucleus
‐ Dendrite – which is a cytoplasmic extension from the cell body, that usually receives information from other neurons and transmits the information to the cell body
‐ Axon – which is a single long cell process that leaves the cell body at the axon hillock and conducts sensory signals to the CNS and motor signals away from the CNS
Typical Nueron
Structural Types of Neurons 1
‐ Multipolar neurons have many dendrites and a single axon. ‐ Most of the neurons within the CNS and nearly all motor neurons are multipolar.
‐ Bipolar neurons have two processes: one dendrite and one axon.
‐ Bipolar neurons are located in some sensory organs, such as in the retina of the eye and in the nasal cavity.
‐ Pseudo-unipolar neurons have a single process extending from the cell body, which divides into two processes as short distance from the cell body.
‐ One process extends to the periphery, and the other extends to the CNS.
‐ The two extensions function as a single axon with small, dendrite-like sensory receptors at the periphery.
Types of Neurons
Glial Cells 1
‐ Glial cells are the supportive cells of the CNS and PNS.
‐Astrocytes serve as the major supporting cells in the CNS. ‐ Astrocytes can stimulate or inhibit the signaling activity of nearby neurons and form the blood-brain barrier.
- Ependymal cells line the cavities in the brain that contains cerebrospinal fluid.
‐ Microglial cells act in an immune function in the CNS by removing bacteria and cell debris.
‐ Oligodendrocytes provide myelin to neurons in the CNS.
‐ Schwann cells provide myelin to neurons in the PNS.
Types of Glial Cells
Myelin Sheath
‐ Myelin sheaths are specialized layers that wrap around the axons of some neurons, those neurons are termed, myelinated axons.
‐ The sheaths are formed by oligodendrocytes in the CNS and Schwann cells in the PNS.
‐ Myelin is an excellent insulator that prevents almost all ion movement across the cell membrane.
‐ Gaps in the myelin sheath, called nodes of Ranvier, occur about every millimeter.
‐ Ion movement can occur at the nodes of Ranvier.
‐ Myelination of an axon increases the speed and efficiency of action potential generation along the axon.
‐ Multiple sclerosis is a disease of the myelin sheath that causes loss of muscle function.
Unmyelinated Neurons
‐ Unmyelinated axons lack the myelin sheaths.
‐ These axons rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in the PNS.
‐ A typical small nerve, which consists of axons of multiple neurons, usually contains more unmyelinated axons than myelinated axons.
Organization of Nervous Tissue
‐ The nervous tissue varies in color due to the abundance or absence of myelinated axons.
‐ Nervous tissue exists as gray matter and white matter.
‐ Gray matter consists of groups of neuron cell bodies and their dendrites, where there is very little myelin.
‐ White matter consists of bundles of parallel axons with their myelin sheaths, which are whitish in color.
Membrane Potentials
‐ Resting membrane potentials and action potentials occur in neurons.
‐ These potentials are mainly due to differences in concentrations of ions across the membrane, membrane channels, and the sodium-potassium pump.
‐ Membrane channels include leak channels and gated channels.
‐ Leak channels are always open, whereas gated channels are generally closed, but can be opened due to voltage or chemicals.
Leak Membrane Channels
‐ Leak channels are always open are and ions can “leak” across the membrane down their concentration gradient.
‐ Because there are 50 to 100 times more K+leak channels than Na+leak channels, the resting membrane has much greater permeability to K+than to Na+; therefore, the K+ leak channels have the greatest contribution to the resting membrane potential.
Gated Membrane Channels
‐ Gated channels are closed until opened by specific signals.
‐ Chemically gated channels are opened by neurotransmitters or other chemicals, whereas voltage gated channels are opened by a change in membrane potential.
‐ When opened, the gated channels can change the membrane potential and are thus responsible for the action potential.
Sodium-Potassium Pump
‐ The sodium-potassium pump compensates for the constant leakage of ions through leak channels.
‐ The sodium-potassium pump is required to maintain the greater concentration of Na+ outside the cell membrane and K+inside.
‐ The pump actively transports K+into the cell and Na+ out of the cell.
‐ It is estimated that the sodium-potassium pump consumes 25% of all the ATP in a typical cell and 70% of the ATP in a neuron.
Resting Membrane Potential 1
‐ The resting membrane potential exists because of: ‐ The concentration of K+ being higher on the inside of the cell membrane and the concentration of Na+ being higher on the outside
‐ Located in the white matter of the CNS are three columns: dorsal, ventral, and lateral.
‐ Columns contain ascending and descending tracts.
‐ Ascending tracts:
- axons that conduct action potentials toward the brain
‐ Descending tracts:
- axons that conduct action potentials away from the brain
Gray Matter in Spinal Cord
‐ The gray matter has a letter H shape with horns.
‐ Posterior horns:
- contain axons which synapse with interneurons
‐ Anterior horns:
- contain somatic neurons
‐ Lateral horns:
- contain autonomic neurons
‐ Central canal:
- fluid filled space in center of cord
Reflexes 1
‐ A reflex is an involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS.
‐ The simplest reflex is the stretch reflex.
‐ A stretch reflex occurs when muscles contract in response to a stretching force applied to them.
‐ The knee-jerk reflex, or patellar reflex is a classic example of a stretch reflex.
‐ The withdrawal reflex, or flexor reflex, is to remove a limb or another body part from a painful stimulus.
‐ The sensory receptors are PAIN RECEPTORS, and stimulation of these receptors initiates the reflex.
Spinal Nerves
‐ Arise along spinal cord from union of dorsal roots and ventral roots
‐ Contain axons sensory and somatic neurons
‐ Located between vertebra
‐ Categorized by region of vertebral column from which it emerges (C for cervical)
‐ 31 pairs (C1-C8, T1-T12, L1-L5, S1-S5, and Co)
Cervical Plexus
‐ Spinal nerves C1-
‐ Innervates muscles attached to hyoid bone and neck
‐ Contains phrenic nerve which innervates diaphragm
Brachial Plexus
‐ Originates from spinal nerves C5-T
‐ Supply nerves to upper limb, shoulder, hand
‐ Axillary nerve - innervates two shoulder muscles and the skin over part of the shoulder.
‐ Radial nerve- posterior arm and forearm
‐ Musculocutaneous- nerve innervates the anterior muscles of the arm and the skin over the radial surface of the forearm.
Lumbosacral Plexus
‐ Originates from spinal nerves L1 to S
‐ Supply nerves lower limbs
‐ Obturator
‐ Femoral
‐ Tibial
‐ Common fibular
Dermatome 1
‐ The nerves arising from each region of the spinal cord and vertebral column supply specific regions of the body.
‐ A dermatome is the area of skin supplied with sensory innervation by a pair of spinal nerves.
‐ Each of the spinal nerves EXCEPT C1 has a specific cutaneous sensory distribution.
Brainstem Components 1
‐ Medulla oblongata
Location:
‐ continuous with spinal cord
Function:
‐ regulates heart rate, blood vessel diameter, breathing, swallowing, vomiting, hiccupping, coughing, sneezing, balance
Other:
‐ Pyramids (enlargements): involved in conscious control of skeletal muscle
‐ Pons
Location:
‐ above medulla, bridge between cerebrum and cerebellum
Function:
‐ breathing, chewing, salivation, swallowing, relay station between cerebrum and cerebellum
‐ Midbrain
Location:
‐ above pons
Function:
‐ coordinated eye movement, pupil diameter, turning head toward noise
Other:
‐ the dorsal part has the four colliculi which are involved in visual and auditory reflexes
Reticular Formation
Location:
‐ scattered throughout brainstem
Function:
‐ regulates cyclical motor function, respiration, walking, chewing, arousing and maintaining consciousness, regulates sleep-wake cycle
Cerebellum
‐ Location:
‐ attached to the brainstem by the cerebellar peduncles
‐ Characteristics:
‐ means little brain
‐ cortex is composed of gyri, sulci, gray matter
‐ Functions:
‐ controls balance
‐ muscle tone
‐ coordination of fine motor
Diencephalon 1
‐ Located between the brainstem and cerebrum
‐ Components:
‐ Thalamus
‐ Hypothalamus
‐ Epithalamus
Diencephalon Components 1
‐ Thalamus
Characteristics:
‐ largest portion of diencephalon
Function:
‐ influences moods and detects pain
Epithalamus:
Location:
‐ above thalamus
Function:
‐ emotional and visceral response to odors
‐ PINEAL GLAND
Hypothalamus
Location:
‐ below thalamus
Characteristics:
‐ controls pituitary gland and is connected to it by infundibulum
Function:
‐ controls homeostasis, body temp, thirst, hunger, fear, rage, sexual emotions
Cerebrum Characteristics
‐ Largest portion of brain
‐ Divisions:
‐ Right hemisphere
‐ Left hemisphere
‐ separated by longitudinal
fissure
‐ Lobes: frontal, parietal,
‐ occipital, temporal,
insula (fifth lobe)
Cerebrum Components
‐ Cerebral Cortex
Location:
‐ surface of cerebrum, composed of gray matter
Function:
‐ controls thinking, communicating,
‐ remembering, understanding, and initiates
‐ involuntary movements
Cerebrum Surface Features
‐ Gyri:
‐ folds on cerebral cortex that increase surface area
‐ Sulci:
‐ shallow indentations
‐ Fissure:
‐ deep indentations
Cerebral Hemispheres
‐ Left hemisphere:
‐ Some tracts are considered indirect because they originate in the brainstem but are indirectly controlled by the cerebral cortex, basal nuclei, and cerebellum.
‐ Tracts in the lateral columns are most important in controlling goal-directed limb movements, such as reaching and manipulating.
‐ Tracts in the ventral columns, such as the reticulospinal tract, are most important for maintaining posture, balance, and limb position through their control of neck, trunk, and proximal limb muscles.
‐ Crossover of axons in the brainstem or spinal cord to the opposite side of the body is typical of descending pathways.
‐ The left side of the brain controls skeletal muscles on the right side of the body, and vice versa.
Basal Nuclei 1
‐ Group of functionally related nuclei
‐ Plan, organize, coordinate motor movements and posture
‐ Corpus striatum:
- deep in cerebrum
‐ Substantia nigra:
- in midbrain
Communication between the Right and Left Hemispheres
‐ Commissures- Connections between the two hemispheres.
‐ Corpus Callosum- largest among commissures, a broad band of nerve tracts at the base of the longitudinal fissure.
Speech
‐ Mainly in left hemisphere
‐ Sensory speech (Wernicke’s area):
parietal lobe
where words are heard and comprehended
‐ Motor speech (Broca’s area):
frontal lobe
where words are formulated
Brain Waves and Consciousness
‐ Used to diagnose and determine treatment for brain disorders
‐ Electroencephalogram (EEG):
‐ electrodes plated on scalp to record brain’s electrical activity
Brain Waves
‐ Alpha waves:
- person is awake in quiet state
‐ Beta waves:
- intense mental activity
‐ Delta waves:
- deep sleep
‐ Theta waves:
- in children
Memory 1
‐ Encoding:
brief retention of sensory input received by
brain while something is scanned, evaluated, and acted up
also called sensory memory
in temporal lobe
lasts less than a second
‐ Consolidated:
data that has been encoded
temporal lobe
short term memory
‐ Storage:
long term memory
few minutes or permanently (depends on retrieval)
‐ Retrieval:
- how often information is used
Types of Memory
‐ Working memory- lasts only a few seconds to minutes and occurs mostly in the frontal cortex. When new information is presented, old information, previously stored in working memory is eliminated.
‐ Short-term memory:
info. is retained for a few minutes to a few days.
Susceptible to brain trauma, such as physical injury
Long-term memory:
can last for a few minutes or permanently
‐ Episodic memory:
- places or events
‐ Learning:
- utilizing past memories
‐ Consolidation- short term transferred to long term by consolidation. The length of time memory is stored may depend on how often it is retrieved and used.
‐ Declarative memory- explicit memory, retention of facts such as names, dates and places. Emotion and mood serve as gates.
‐ Procedural memory- reflexive memory, development of motor skills, such as riding a bicycle. Only small amount of procedural memory is lost over time.
Limbic System and Emotions 1
‐ The olfactory cortex and certain deep cortical regions and nuclei of the cerebrum and the diencephalon are grouped together under the title limbic system.
‐ The limbic system influences long-term declarative memory, emotions, visceral responses to emotions, motivation, and mood.
‐ A major source of sensory input to the limbic system are the olfactory nerves.
‐ The limbic system is connected to, and functionally associated with, the hypothalamus.
‐ Lesions in the limbic system can result in voracious appetite, increased (often perverse) sexual activity, and
docility (including loss of normal fear and anger responses).
Meninges 1
‐ The meninges are three connective tissue layers that surround the brain and spinal cord.
‐ The outermost (most superficial) meningeal layer is the dura mater, which is the toughest of all the meninges.
‐ The dura mater forms two layers around the brain and only one layer around the spinal cord.
‐ The second meningeal membrane is the very thin, wispy arachnoid mater.
‐ The space between the dura mater and the arachnoid mater is the subdural space, which is normally only a potential space containing a very small amount of serous fluid.
‐ Cerebrospinal fluid is and blood vessels are found in the subarachnoid space.
‐ The third meningeal membrane, the pia mater, is very tightly bound to the surface of the brain and spinal cord.
Ventricles 1
‐ The CNS contains fluid-filled cavities, called ventricles.
‐ Each cerebral hemisphere contains a relatively large cavity called the lateral ventricle.
‐ The third ventricle is a smaller, midline cavity located in the center of the diencephalon between the two halves of the thalamus and connected by foramina (holes) to the lateral ventricles.
‐ The fourth ventricle is located at the base of the cerebellum and connected to the third ventricle by a narrow canal, called the cerebral aqueduct.
‐ The fourth ventricle is continuous with the central canal of the spinal cord.
‐ The fourth ventricle also opens into the subarachnoid space through foramina in its walls and roof.
Cerebrospinal Fluid
‐ Cerebrospinal fluid (CSF) bathes the brain and spinal cord, providing a protective cushion around the CNS.
‐ The ependymal cells located in the choroid plexuses of the ventricles produce the CSF.
‐ CSF fills the brain ventricles, the central canal of the spinal cord, and the subarachnoid space.
‐ The CSF flows from the lateral ventricles into the third ventricle and then through the cerebral aqueduct into the fourth ventricle.
‐ A small amount of CSF enters the central canal of the spinal cord.
‐ The CSF exits the fourth ventricle through small openings in its walls and roof and enters the subarachnoid space.
‐ Masses of arachnoid tissue, called arachnoid granulations, penetrate the superior sagittal sinus, a dural venous sinus in the longitudinal fissure, and CSF passes from the subarachnoid space into the blood through these granulations.
Cranial Nerves 1
‐ 12 pair of cranial nerves
‐ Named by roman numerals
‐ 2 categories of functions: sensory and motor
‐ Cranial Nerve I (Olfactory) is a pure sensory nerve for smell
‐ Cranial Nerve II (Optic) is a pure sensory nerve for vision
‐ Cranial Nerve III (Occulomotor) is a pure motor nerve for eye movement
‐ Cranial Nerve IV (Trochlear) is a pure motor nerve for eye movement
‐ Cranial Nerve V (Trigeminal) is both a motor and sensory nerve. It is sensory for pain, touch, and temperature for the eye and lower and upper jaws. It is motor for muscles of chewing.
‐ Cranial Nerve VI (Abducens) is a pure motor nerve for eye movement
‐ Cranial Nerve VII (Facial) is both a sensory and motor nerve. It is sensory for taste and motor for facial expression.
‐ Cranial Nerve VIII (Vestibulocochlear) is a pure sensory nerve for hearing and equilibrium
‐ Cranial Nerve IX (Glossopharyngeal) is both a motor and sensory nerve. It is sensory for taste and motor for swallowing.
‐ Cranial Nerve X (Vagus) is both a motor and sensory nerve. It is sensory and motor for organs in the thoracic and abdominal cavities.
‐ Cranial Nerve XI (Accessory) is a pure motor nerve for the trapezius, sternocleidomastoid, and muscles of the larynx.
Cranial Nerve XII (Hypoglossal) is a pure motor nerve for the tongue
Nervous System Notes
Course: Nursing (RLE70)
University: Capitol University
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