Nervous System: Functions and Components

Nervous System Functions

• The nervous system is the body's master controlling and communicating system
• It communicates via chemical and electrical signals
• Functions include sensory input, integration, and motor output
• Sensory receptors gather information about internal and external changes
• Integration involves processing and interpreting sensory input
• Motor output activates effector organs like muscles and glands to produce a response
• The sequence is Sensory input -> Integration (in brain) -> Motor Output

Components of the Nervous System

• Structurally and functionally, the nervous system includes the Central Nervous System (CNS) and Peripheral Nervous System (PNS)
• The CNS comprises the brain and spinal cord within the dorsal body cavity
• The CNS interprets sensory input and determines motor output
• The PNS consists of nerves extending from the brain and spinal cord
• Spinal nerves connect to and from the spinal cord
• Cranial nerves connect to and from the brain
• The PNS is the portion of the nervous system outside the CNS
• Sensory division: carries impulses from the skin, skeletal muscles, and joints to the CNS
• Motor division: transmits impulses from the CNS to effector organs
• Somatic nervous system: controls voluntary organs and skeletal muscle
• Autonomic nervous system: controls involuntary organs, including the heart muscle

Neuroglia in CNS and PNS

• Most neuron cell bodies are located in the CNS
• There are 6 types of neuroglia: 4 in the CNS and 2 in the PNS
• CNS neuroglia include astrocytes, microglial cells, ependymal cells, and oligodendrocytes
• PNS neuroglia include satellite cells and Schwann cells

CNS Neuroglia:

• Nuclei: Clusters of neuron cell bodies in the CNS, containing both neuron cell bodies and their processes
• Tracts: Bundles of neuron processes in the CNS that connect the brain and spinal cord
• Astrocytes: Protect neurons and form the blood-brain barrier; most abundant and highly branched
• Microglial Cells: Can transform to phagocytize microorganisms and neuronal debris
• Ependymal Cells: Line the central cavities of the brain and spinal cord, forming a permeable barrier between cerebrospinal fluid (CSF) and CNS cells
• Oligodendrocytes: Form the myelin sheath in the CNS without regeneration properties

PNS Neuroglia:

• Ganglia: Clusters of neuron cell bodies in the PNS, containing only neuron processes
• Nerves: Bundles of neuron processes in the PNS
• Satellite Cells: Surround neuron cell bodies in the PNS, similar in function to astrocytes
• Schwann Cells: Can regenerate and form myelin sheaths around peripheral nerve fibers

Neuron Processes

• Two types of neuron processes: dendrites and axons
• Dendrites: Accept and conduct neural impulses
• Axons: Long and covered with myelin sheath for faster electrical impulses

Neuron Structure and Function

• Dendrites: Branch-like structures
• Axon: Long cord-like structure
• Cell Body: Center from which dendrites originate

White and Gray Matter

• White matter: Myelinated parts of neurons, forming tracts to axons and connecting different brain parts
• Gray matter: Unmyelinated cell bodies and dendrites, transmitting information between brain and body parts

Neuron Classification

• Neurons are classified structurally and functionally

Structural Classification:

• Multipolar: Multiple processes, one axon and several dendrites; most common in the CNS
• Bipolar: Two processes, one axon and one dendrite; rare
• Unipolar: One T-like process with two axons; also known as pseudounipolar

Functional Classification:

• Sensory (Afferent): Transmit impulses from sensory receptors to the CNS and are unipolar with cell bodies in ganglia in the PNS
• Motor (Efferent): Carry impulses from the CNS to effectors; multipolar with most cell bodies in the CNS
• Interneurons: Association neurons intermediate between motor and sensory neurons, shuttle signals through CNS pathways, located in the CNS (99% of body neurons)

Neurolemma and Myelin

• Neurolemma and myelin are involved in nerve cell regeneration

Resting Membrane Potential

• Neural cells do not need an impulse to stimulate their voltage

Resting Membrane Potential Depends On:

• Differences in K+ and Na+ concentrations inside and outside of the cells
• Differences in permeability of plasma membranes to these ions
• Most anions cannot leave the cell because the cell wants to be negative
• Na+/K+ pumps

Ion Channels:

• Leakage Channels: Alternate between open and closed
• Types of channels: K+ channels > Na+ channels
• Action: Randomly open and closed

Ligand Gated Channels:

• Ligand-Gated Channels: Respond to chemical stimuli where the ligand binds to a receptor; opens the channel

Mechanically Gated Channels:

• Mechanically Gated Channels: Respond to mechanical vibration or pressure stimuli; stimulus opens the channel

Voltage Gated Channels:

• Voltage Gated Channels: Respond to direct changes in membrane potential
• Status Depends On: Open or closed state depends on electrical current
• Activity: Open at -50 mV, closed at -70 mV; changes in membrane potential open the channel

Resting Membrane Potential Characteristics

• Unequal distribution of ions across the membrane and selective permeability of neuron membrane to Na+ and K+

Voltage and Ion Distribution

• The mechanism of nerve impulse transmission along a neuron involves changes in voltage and ion distribution

Graded Potentials and Action Potentials

• Graded Potential: Short arrow communication but allows long messages to happen, and the short arrows go over the interneurons
• Communication: Interneurons, only in the CNS, receive impulses sent from sensory neurons and conduct them
• Nerve Action Potential: Electrical impulse that carries the message

Graded Potentials

• Small deviations in resting membrane potential that are short-lived and localized
• Strength: Stronger stimulus = more voltage flows and farther current flows
• Stimulus: Triggered by a stimulus which opens gated ion channels
• Actions: Results in depolarization (becomes more positive) or hyperpolarization (becomes more negative)
• Origination: Develops on the cell body and dendrites
• Triggers: Occurs in response to the opening of mechanically gated or ligand gated ion channels
• Summation: Can be added together to become larger in amplitude

Action Potentials

• A sequence of rapidly occurring events that decrease and reverse membrane potential (depolarization) and restore the resting state (depolarization)
• Function: Main way neurons send signals

Action Potential Properties:

• Same Strength: All have the same strength once they reach the threshold and involves the opening of specific voltage-gated channels
• Channel Properties:
  • Axon = only point of the neuron with voltage-gated channels
  • Sodium VG = fast response time
  • Open = Na+ moves into the cell
  • When reaches 0 or +, channel closes
  • K+ channel = SLOW
• Absolute Refractory Period: Most action potential channels are still open, no other action potential is possible
• Relative Refractory Period: -45 mV creates a chance for action potential to happen if above or below threshold

Threshold Phenomenon

• Membrane is depolarized by 15 to 20 mV
• Na+ permeability increases
• Na+ influx exceeds K+ efflux (leaving cell)
• An action potential either happens completely or does not happen at all

Absolute Refractory Period

• Voltage-gated Na+ channel activation gates are open

Relative Refractory Period

• Voltage-gated K+ channels are open, Na+ channels are in the resting state

Synapses

• List and describe the components of a synapse and its function and define presynaptic neuron and postsynaptic cell
• Electrical Snap:
  • Gap junctions connect cells
  • Allows transferring of information to synchronize activity of a group of cells
• Chemical Synapse:
  • Majority in CNS and PNS
  • One way transfer of information from a presynaptic neuron to a postsynaptic neuron
• Postsynaptic:
  • Neurotransmitter receptors cause graded potentials to vary in strength via the amount of neurotransmitter released as well as the neurotransmitter staying in the cleft

Neurotransmitters and Potential

• Describes the mechanism of conduction of an action potential across a synapse and the function of neurotransmitter of the effects of excitatory and inhibitory neurotransmitters

Excitatory Postsynaptic Potentials (EPSP):

• More Depolarizing (Positive)
• Neurotransmitter binding causes chemically gated channels to open (Na and K can flow in opposite directions)
• Na+ influx > K+ efflux, causing the depolarization to be more positive inside the cell than out
• Characteristics: Can trigger action potential if EPSP is of threshold strength
• Glutamate: Excitatory neurotransmitter
• ACh excitatory at neuromuscular junction in skeletal muscle

Inhibitory Postsynaptic Potentials (IPSP):

• More Hyperpolarizing (Negative)
• Neurotransmitter binding opens chemically gated ion channels
• Postsynaptic Actions: Make the postsynaptic membrane more permeable to K+ or Cl-
  • If K+ channels open: It moves out of the cell
  • If Cl- channels open: It moves into the cell
• Actions: Reduces the post-synaptic neuron's ability to produce an action potential and move the neuron further away from the threshold
• Inhibitory Neurotransmitters: GABA and glycine
• Note: ACh is inhibitory in cardiac muscle

Multiple Sclerosis

• Myelin sheath in the CNS is destroyed when the immune system attacks
• CNS Actions: Little to no repair
• PNS Actions: Repair is possible if the cell body is intact

Brain Regions

• The brain is divided into four regions: Cerebral hemispheres, Diencephalon, Cerebellum, Brainstem

Cerebellum:

• occupies inferior and posterior aspects of the cranial cavity
• has two hemispheres and a central vermis connected by central vermis
• maintains normal muscle tone, posture and balance

Brainstem:

• white= myelated
  • 1. arbor vitae. specific name for white matter in cerebellum
• gray = unmyelated
  • Midbrain:
    • Aqueduct of the midbrain (cerebral aqueduct): passageway connects 3+4 ventricles
  • Pons
  • Medulla oblongata

Brain Protection

• cranial bones
• cranial meninges
  • pia, arachnoid, dura matter (2 layers)
  • periosteal and meningeal layer
  • “tough mother”
  • forms partitions to separate and stabilize parts of the brain
  • limits excessive movement of the brain
  • contains pain receptors
  • Tentorium Cerebelli
    • roof over cerebellum: small cavity to fit cerebellum
• cerebrospinal fluid: nourishment and protection

Complications

• Epidural hematoma: fast to develop
• Subdural hematoma: from blood trauma: slowly to develop; blood accumulates between dura - asymptomatic

Cerebrospinal Fluid (CSF)

• Liquid that protects the brain and spinal cord against chemical and physical injuries; carries oxygen, glucose, and other important substances from blood to nervous tissue cells
• Forms in the lateral ventricles
• The fourth ventricle has openings to move fluids circulates in the CNS
• Similar to blood plasma (filtered from blood plasma) but less protein
• Continuously produced in the brain ventricles and reabsorbed in arachnoid villi
• Projections: Are knoblike projections that protrude superioly through the dura mater to absorb CSF into venous blood
• Used to diagnose diseases, using a spinal tap

Blood Brain Barrier (BBB)

• Neuralgia form warp around blood vessels
• Protects brain cells from harmful substances and pathogens
• Serves as selective barrier to prevent passage of substances into the brain
• Can prevent entry of therapeutic drugs

Brain Stem

• Includes the Medulla, Pons, Midbrain, Thalamus, Hypothalamus, Limbic System, RAS

RAS:

• Reticular Activation System is a region involved in maintaining consciousness
• inhibited: sleep
• depressed: alcohol, tranquilizers
• severe injury: coma because neurons will no longer send a message to maintain consciousness

Medulla Oblongata:

• Continues with the superior aspect of the spinal cord and contains portions of both motor and sensory tracts (CNS)

Crinal Nerves:

• vestibulocochlear and hypoglossal tracts ( motor and sensory tracts)
  • connects up with motor neurons and lower motor neurons
    • decussation of pyramids crossing where moto descending and inferior olivary nuclei
  • functional regions: group of neurons that can control
    • heart rate (why brain stem damage can cause cardiac arrest)
    • respiratory rate
    • swallowing
    • coughing

Pons:

• Continuous myelinated axons
  • connects cerebellum (movements) to rest of brain
  • located superior to medulla oblongata
  • links parts of the brain with one another with tracts
  • relays nerve impulses to voluntary skeletal muscle movements from cerebrum to cerebellum
  • pneumotaxic and apneustic areas (control of respiration)

Midbrain:

• located superior to medulla oblongata and extends from the pons to the diencephalon
  • structures regions:
    • cerebral peduncles corpa quadrigemina (4 bodies together)
    • regulates auditory (ex. moving head towards a noise) and visual reflexes

Diencephalon:

• Between brainstem and cerebellum
  • Thalmus receives impulses from ALL receptors EXCEPT smell
  • located superior to midbrain
  • contains nuclei that serve as relay stations for all sensory impulses (except smell) to the cerebral cortex
• Hypothalamus= H for homeostasis
  • located inferior to the thalamus
  • has 4 major regions
  • controls many body activities
  • master control of ANS
    • body temp, hunger, weight, digestive secretions, thirst, hormone secretions, self, sexual functions

Epithalmus:

• located superior and posterior to the thalmus
  • contains the pineal gland
    • secretes melatonin and habenuclar nuclei (involved in olfaction)

Limbic System:

• Located in cerebrum diecephalon " emotional brain"
  • Amygdala recognizes angry facial expressions\
    • Assesses danger
  • Hippocampus: Crucial for acquiring new memories

Hydrocephalus

• Ventricles of the brain contain CSF and choroid plexuses make CSF
• Choroid Plexus: Lines cavities epedemine is the cell forming choroid plexus in the ventricles of the brain

Flow of CSF (Chart)

• Lateral ventricle choroid plexuses: CSF flows into lateral ventricles goes through interverticluar foramina
• Enters into third ventricle and third ventricles choroid plexus flows CSF into third ventricle
• Throught aqueduct of the midbrain
• Fourth Ventricle: Goes to the fourth ventricle and fourth ventricles choroid plexus flows CSF into fourth ventricle
• Goes to: Through lateral and median apertures into subarachoid space in which the subarachnoid space lies between arachnoid and plamator of meninges
• 10. into arachnoid villi of dural venous sinuses
• 11. into venous blood
• 12. into heart and lungs
• 13. flows back through arterial blood and into the ventricles again

Hydrocephalus (Disease)

• Presents At Birth: "water in brain"
• Fluid builds up inside the brain
• Blocked By: CSF circulatory pathway is blocked by tumor or birth defect
• Treatment: Shunt implanted to drain fluid to another body cavity
• Identify and discuss basal ganglia of the brain and briefly describe Parkinson's Disease

Basal Ganglia

• Paired masses of gray matter in each cerebral hemispheres
• Function controls regulates voluntary movements

Parkinson's Disease

• degeneration of dopamine releasing neurons of substantia nigra:
• basal nuclei deprived of dopamine become overactive = tremors at rest with function decribed

Cerebrum (Structures)

• Largest portion of the brain and is composed of gray matter
• Contains gyri, fissures, and sulci on the cerebral cortex: "executive suite" of the brain
  • site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding with its features

Cerebral Cortex

• thin superficial layer of gray matter WITHOUT axons
• deep to the cortex is white matter and composed of tracts of neurons: connects parts of the brain to each other and the spinal cord
• contains bundle of white matter tracts: corpus callosum which connects the right and left hemispheres of the cerebrum

Hemispheres:

frontal lope, parietal lobe, temporal lobe, occipital lobe, insula

Cortext Functions

• Discuss the structure and function of cerebral cortex and identify lobes and areas responsible for speech, sensory, motor control, hearing, olfaction, vision
• Sensory Areas: includes primary somatosensory cortex is located in post central gyri of parietal lobe
• Functions in: receives general sensory information from skin, proproceptors of skeletal muscles, joints, and tendons

Somatosenory Associated Cortex:

• located posterior to primary somatosensory cortext
  • actions integrates sensory input from primary somatosensory corext for understanding of an object

Primary Visual Cortext:

• located on extreme posterior tip of occipital lobe
• recieves visual info from retinas
  • Motor Areas: and located
• premotor cortex: - helps plan movements: skilled motor activities
• controls learned, repetitious, or patterned motor skills

Broca's Area:

• present in one hemisphere
  • motor speech area: directs muscles of speech productions
  • active in planning speech and voluntary motor activities Frontal Eyes Field: - Controls volunatry eye movements

Spinal Cord

• Identify and locate the spinal meninges and associated spaces discussing their functions
• Componets spinal cord enclosed in vertebral column and consists of structure
  • begins: foramen magnum structure in skull
  • ends function at L1 or L2 vertebra
  • begins as extention of the medulla oblongata and is described through process

Spinal Cord Functions

• functions: processes reflexes; integrates EPSPs and IPSPs; conducts sensory impulses to the brain and motor impulses to effectors

Spinal Cord Protection

bone (vertebrae) and connective tissue (meninges): 3 layers with structures of epidural

• Dura mater ,arachnoid mater, Pia mater and fluid (CSF) fills subarachnoid space between arachnoid and pia maters

Structures of Spinal Cord

• epidural space and lumbar puncture, Epidural space and cushion of fat and network of veins in space between vertebrae and spinal dura mater - dural and arachnoid membranes extend to sacrum, BEYOND end of cord with the site (site of lumbar puncture or tap)
• Describes the flow and location of CSF in the spinal cord discuss the composition and functions of cerebrospinal fluid.

Spinal Cord Structure

• Grey in core and Matter is outside and structure
• recieves integrates incoming and outgoing information to perform spinal reflexes and includes following horns

Dorsal Horns:

• interneurons that recieves somatic and visceral sensory input - ventral horns: some interneurons; somatic moto neurons - lateral horns and action: ONLY in thoracic and superior lumbar regions. sypathetic neurons - ventral roots: : bundle of motor neuron axons that exit the spinal cord with function - dorsal roots: sensory input to cord and the function of these areas located - white matter. - tracts tracts conduct nerve impulses to and from the brain and are shown through action

Neurons of Spinal Cord

• Discuss the location of interneurons, cell bodies, axons, and dendrites of afferent and efferent neurons in the spinal cord and relationship to the function of
  • Afferent neurons carries sensory information to the brain/spinal cord
  • efferent neuron: carriers motor information away from the brain/spinal cord
  • Deceribe the of ascending descend pathway in spinal

Spinal Nerves

• Ascending: body to brain including sensations( touch pain etc)
• Descending: transmits motor commands from brain to muscles
• Can desrupt these pathways by spinal cord injury leading to sensory below

Spinal Nerve Structures

• Roots: Each spinal nerve originates from two nerve roots within the spinal cord: the dorsal root (sensory) carrying afferent signals from the periphery to the spinal cord, and the ventral root (motor) carrying efferent signals from the spinal cord to muscles.
• ganglion
• fusion
• mixed nerve

Important Components

• nerve plexuses: A nerve plexus is a network formed by the interweaving of spinal nerve branches, allowing for complex innervation patterns to different body regions by combining fibers from multiple spinal nerves.
• Cervical Plexus: Located in the neck, supplying the neck muscles and skin of the head and neck.
• Brachial Plexus: Found in the shoulder region, providing innervation to the arm, forearm, and hand.
• Lumbar Plexus: Located in the lower back, innervating the anterior thigh and part of the lower abdomen.
• Sacral Plexus: Situated in the pelvis, supplying the posterior thigh, leg, and foot.

Nerves of the Plexus

• Phrenic Nerve: Originates from the cervical spinal nerves (C3, C4, and C5) and primarily innervates the diaphragm, which is crucial for breathing.
• Radial Nerve: Arises from the posterior cord of the brachial plexus (C5-T1), supplying the muscles of the posterior arm and forearm, as well as providing sensation to the back of the hand.
• Ulnar Nerve: Also from the brachial plexus (C8 and T1), innervating the muscles of the hand and providing sensation to the medial aspect of the hand and fingers.
• Sciatic Nerve: A major nerve of the sacral plexus, formed from the lumbar spinal nerves (L4, L5) and sacral nerves (S1, S2, S3), supplying the muscles and skin of the posterior thigh and lower leg.
• Femoral Nerve: Originates from the lumbar plexus (L2, L3, and L4), innervating the muscles of the anterior thigh and providing sensation to the anterior thigh and knee.

Neuronal Relays

• Discusses the structural and functional components of two and three-neuron reflex arcs.
• Reflex: Fast, involuntary and unplanned in response to stimulous
• The spinal cord is a fast response

Three Neuron Reflexes

• two, sensory neuron, axon conducts from receptors integrating center
• three integ center or regions whitin CNs relays

Nerve Classifications

• Discuss nerve class using: monosynaptic ,polysynaptic,ipsilateral,contralateral,mono-

• Ipsilateral- is in the same side

• Contralateral is in opposite side

• Mono is when inolvves

• Polysym when involvss interneuron

• Reclipriacl when interneron inihibt

Autonomic System

• Describe the structure and function of the divisions of the autonomic nervous system including the location of the preganglionic neuron cell bodies in the CNS and postganglionic neuron cell bodies in autonomic ganglia, neurotransmitters, receptors and effectors.
  • SOmatic is Sensory and motor
  • Autonomic receive input and series of motor Divinded into 2.

Autonomic Nervous System Structures:

• Sympatheic ns: fight or flight- stim leads ready
• Think being symathic and getting ready
• Parasymath: help

Ganglia Structures

• sympathetic trunk ganglia. and prevertebal : paraseympath
• Autonomic: controls volunatry of skateal muscle
• differemce betwen motor, the leng and the nTS

ANS NT and Recpetors

• Compare the functions of adrenergic and cholinergic fibers and receptors
• NT NT either cholineneric or adgrenergic
  • Released at all Parasymapathet