Introduction to the Nervous System

The Nervous System: An Introduction

• The nervous system is the body's main control and communication network
• Its cells use electrical signals for rapid communication
• Collects, analyzes, and responds to information from both internal and external environments to maintain homeostasis

Peripheral Nervous Systems

• Includes all neural elements outside the spinal cord
• Responsible for relaying information back to the nervous system

Motor Division

• The Somatic system controls skeletal muscle contraction, enabling voluntary movements
• The Autonomic system automatically controls smooth muscle and cardiac muscle functions

Organization of the Nervous System

• The nervous system is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)

Afferent/Efferent

• Afferent neurons bring sensory information to the brain
• Efferent neurons carry motor commands away from the brain, enabling responses

Neurons and Glial Cells

• Nervous tissue has two primary cell types: neurons and glial cells
• Neurons are excitable cells that use electrical signals to communicate as nerve cells
• Glial cells support and protect neurons

Neuron Functions

• Neurons have sensory and motor functions
• Neurons can be interneurons

What are Neurons

• They are the structural units of the nervous system
• In neurons, messages are conducted as electrical signals between body parts, facilitated by changes in membrane potential

Neuron Characteristics

• Neurons are amitotic, meaning they do not duplicate or divide
• Neurons need a continuous supply of oxygen and glucose due to a high metabolic rate

Neuron Structure: Tendrils

• A cell body contains the nucleus, plus most organelles for neurons
• The cell body organelles are concentrated in the CNS and are protected

Neuron Structure: Axon

• Axons are specialized membranous processes that are often insulated with a myelin sheath
• Ion channels are located in the Nodes to propagate

Structure of a Neuron

• Dendrites are fibers projecting from the cell body, receiving information from other neurons
• The cell body houses the nucleus and biological machinery to keep the cell alive
• Axons are transmitting messages through a neuron
• Axon terminals are at the axon's end, sending messages to other neurons

Neuron vs. Nerve

• A nerve is a collection of neurons and bigger in size
• Neurons are specialized and microscopic

The Neuroglia

• Neuroglia (glial cells) are non-neuronal cells supporting the CNS and PNS
• Neuroglia functions include homeostasis, structure, protection, immune response, development, and synapse formation

Membrane Potential

• The voltage difference across the plasma membrane is due to the separation of charged particles (ions)
• Sodium (Na⁺) and Potassium (K⁺) are key ions in membrane potential

Potassium's Role (K⁺)

• K⁺ diffuses out of the cell due to the concentration gradient
• Negatively charged anions (A⁻) remain inside, the electrical force pulls K⁺ back inside
• This balance creates the Resting Membrane Potential at -70mV

Sodium's Role (Na⁺)

• Na⁺ diffuses in due to the concentration gradient
• The negative charge inside also attracts Na⁺
• The membrane is 75 times more permeable to K⁺ than Na⁺ causing a net negative charge inside

Action Potentials

• Action potentials result from membrane potential changes due to ion channel activity
• Chemically-gated channels open when neurotransmitters bind
• Voltage-gated channels open when a specific membrane voltage is reached

Threshold

• The threshold for initiating an action potential is between -55mV and -60mV
• Action potentials start at the axon hillock, which has a high density of Na⁺ channels
• Only a graded potential occurs if the stimulus doesn't reach the threshold

Phases

• Depolarization occurs when Na⁺ enters, making the inside more positive
• Repolarization occurs when K⁺ leaves, which restores the negative charge
• Hyperpolarization occurs when excess K⁺ leaves, causing the cell to become more negative
• The Na⁺-K⁺ pump restores balance, returning the cell to its resting potential

Propagation of Action Potentials

• Action potentials travel along axons to transmit signals

Types of Propagation

• Continuous conduction occurs in unmyelinated axons
• Saltatory conduction, found in myelinated axons, is faster due to jumping from node to node

Synaptic Transmission

• A presynaptic neuron releases neurotransmitters at the synapse
• Neurotransmitters then cross the synaptic cleft and bind to postsynaptic receptors
• Signals can be excitatory (EPSP) or inhibitory (IPSP)

Summation of Postsynaptic Potentials

• Temporal Summation: Multiple signals from one neuron in a brief period.
• Spatial Summation: Simultaneous signals from multiple neurons.

Key Takeaways

• Resting Membrane Potential is -70mV
• Action Potential Threshold is -55mV
• Na⁺ entry causes Depolarization
• K⁺ exit causes Repolarization
• Too negative is Hyperpolarization
• Resting potential is restored with the Na⁺-K⁺ pump
• Signals are propagated through axons and synapses

Spinal Cord Overview

• The spinal cord is cylindrical in shape
• It occupies the upper two-thirds of the vertebral canal
• Continuation of the Medulla Oblongata is through the Foramen Magnum
• In adults, the spinal cord terminates at L1-L2 forming the conus medullaris
• At birth, the spinal cord ends around L3
• In the fetus (3rd month), the spinal cord extends the vertebral column's full length

Spinal Cord Organization

• The spinal cord is protected by the vertebral column
• There are 31 pairs of spinal nerves
• 8 cervical
• 12 thoracic
• 5 lumbar
• 5 sacral
• 1 coccygeal
• Enlargements include: cervical for upper limb control and lumbar for lower limb control
• The Cauda Equina ("horse’s tail") is a bundle of spinal nerves that extends below the conus medullaris

White and Gray Matter

• Neuron cell bodies and glial cells are contained in the Gray matter
• Myelinated and unmyelinated axons are contained in the White Matter

Gray Matter Organization: Horns

• Posterior Gray Horn receives somatic and visceral sensory input
• Lateral Gray Horn, only in thoracic and lumbar regions, provides visceral motor control
• Anterior Gray Horn provides somatic motor control

White Matter Organization: Columns

• The Posterior White Column resides between the posterior gray horn and the posterior median sulcus.
• The Lateral White Column is located between the posterior and anterior gray horns.
• The Anterior White Column sits between the anterior gray horn and the anterior median fissure.

Spinal Nerve Structure

• Spinal nerves contain mixed fibers (sensory and motor)
• Exit locations of the spinal nerves: C1-C7 are located above, C8 is below C7, T1-L5 located below, S1-S4 exit through the Sacral Foramina, and S5 & Coccygeal pass through the Sacral Hiatus

Spinal Nerve Roots

• The Dorsal (Posterior) Root is Afferent, carrying sensory signals to the spinal cord.
• The Ventral (Anterior) Root is Efferent, sending motor signals out of the spinal cord
• Spinal nerves are formed when Dorsal and Ventral Roots unite

Spinal Cord Divisions

• The Dorsal (Posterior) Ramus innervates the back muscles and skin
• The Ventral (Anterior) Ramus innervates the limbs and the anterior/lateral trunk

Ascending and Descending Tracts

• Ascending Tracts carry sensory information to the brain
• Descending Tracts carry motor commands from the brain

Meninges

• The Dura Mater ("Tough Mother") is the outer layer
• The Arachnoid Mater ("Web-like Mother") is the middle layer
• The Pia Mater ("Delicate Mother") is the inner layer that touches the spinal cord

Dermatomes & Plexuses

• A Dermatome is a region of skin supplied by a single spinal nerve
• The Cervical Plexus supplies the head, neck, and diaphragm
• The Brachial Plexus supplies the upper limb
• The Lumbosacral Plexus supplies the lower limb

Blood Supply

• The main supply of blood is via the Anterior Spinal Artery
• Two Posterior Spinal Arteries also supply it
• Radicular Arteries branch out coming from the intercostal and lumbar arteries
• Six longitudinal veins drain in to the internal vertebral venous plexus
• Occlusion of the Anterior Spinal Artery results in Paraplegia and Incontinence

Spinal Nerve Injuries

• Common causes are spondylosis, intervertebral disc prolapse, and sciatica in the lumbar region

Key points for spinal cord

• Spinal cord terminates at vertebral levels L1-L2 in adults
• Thirty-one pairs of spinal nerves control various functions of the body
• Dorsal roots are sensory and ventral roots are motor
• White matter comprises axons, while gray matter contains cell bodies
• Dermatomes provide a map of sensory regions of the nerves
• Proper blood supply is essential for the proper function of the spinal cord

Brain Overview

• Key Brain Regions: includes cerebral hemispheres, diencephalon, brainstem, and cerebellum
• The brain is protected by cranial meninges (dura mater, arachnoid mater, and pia mater)

Brain Ventricles

• Ventricles circulate cerebrospinal fluid (CSF)
• Lateral ventricles appear in each hemisphere
• The third ventricle is located in the diencephalon
• The fourth ventricle appears in hindbrain and is connected to spinal cord

Cerebral Hemispheres

• Key surface features are Gyri (ridges), Sulci (shallow grooves), and Fissures (deep grooves separating hemispheres)
• Six Lobes: frontal, parietal, temporal, occipital, insula, and limbic

Functional Lobes

• The frontal lobe controls motor function, plus decision-making.
• The parietal lobe is for sensory data processing
• The temporal lobe handles memory plus hearing
• The occipital lobe handles vision
• The insula covers internal organ awareness The limbic lobe handles memory plus emotions

Cerebral Cortex

• The cerebral cortex is 2-4 mm thick, with 40% of the brain's mass
• Control is contralateral, meaning that the left hemisphere controls the right side of the body, and vice versa
• Lateralization is when some functions are dominant in one hemisphere

Motor Areas

• These control voluntary movements
• Primary motor cortex handles precise movement
• Premotor cortex coordinates and also plans movement
• Broca’s handles speech production
• Frontal handles eye movement

Sensory Areas

• Processing of sensory information is acheived through these areas
• Primary somatosensory handles touch as well as proprioception signals
• Somatosensory controls texture, size, plus interpretation
• Visual, auditory, and olfactory areas are for vision, sound, and smelling processing
• The Gustatory cortex perceives taste Visceral processes organ awareness and the Vestibular handles balance and spatial orientation

Association Areas

• The higher order functions come from it
• Prefrontal handles cognition, including judgement plus personality
• Posterior has pattern and facial recognition
• Limbic handles memory, emotion, and formation

Autonomic Nervous System (ANS)

• The sympathetic system enables fight or flight, plus increases heart rate, respiration, and blood flow to skeletal muscles
• Parasympathetic system reduces heart rate and blood pressure, plus stimulating energy storage and digestion
• The hypothalamus controls ans activities

Dual Innervation

• Most organs have a balance of both parasympathetic and sympathetic input
• Exceptions include vasomotor function in blood vessels, sudomotor function in sweat glands, and pilomotor function in hair

Key Takeaways for the brain

• Key Regions include cerebrum, plus cerebellum, brainstem, and diencephalon.
• Cerebral cortex controls higher functions for thinking, sensation, and voluntary movement actions
• Motor areas control movement and sensory areas intake imput The autonomic system regulates various involuntary action functions
• Sympathetic corresponds to stress and Parasympathetic corresponds to relaxation

Cranial Nerves

• There are 12 cranial nerves, and they emerge straight from the brainstem and the brain from the spinal cord instead The cranial nerve functions and actions are the sensory and motor, plus autonomic controlling of the internal organs, neck, and head

Cranial Nerves and their Functions

• Olfactory Nerve (I) handles sensory smelling
• Optic Nerve (II) handles sensory vision
• Oculomotor Nerve (III) handles motor eye movement plus pupil constriction
• Trochlear Nerve (IV) handles motor eye movement
• Trigeminal Nerve (V) handles sensory face sensation, and both chewing
• Abducens Nerve (VI) handles motor eye movement
• Facial Nerve (VII) handles both taste, and facial expression
• Vestibulocochlear Nerve (VIII) handles sensory balance, as well as hearing
• Glossopharyngeal Nerve (IX) handles both swallowing, as well as taste
• Vagus Nerve (X) controls parasympathetic side of organs
• Accessory Nerve (XI) handles motor neck plus shoulder
• Hypoglossal Nerve (XII) handles tongue movement

Reflexes

• Reflexes correspond to stimuli to involuntary response
• Integration occurs in the spinal cord, instead of the brain

Reflex Arc Components

• The Receptor detects the stimulus
• The Sensory Neuron gives brain data to spinal cord
• The Integration center processes the response
• The Motor Neuron sends output to muscles
• The Effector carries out the response of the glands or muscle

Types of Reflexes

• Exteroceptive handles external stimuli
• Withdrawal, thrust, withdraw, plus vestibulo-ocular reflexes
• Proprioceptive handles the body position
• Stretch, as well as golgi tendon reflexes
• Visceral handles autonomic functions The sensory receptors in reflexes are exteroceptors, interoceptors, as well as proprioceptors

Key Notes

• The cranial nerves control the head, neck, plus internal working actions
• A quick, direct response occurs from nerve reflexes
• Spinal reflexes transpire when the brain doesn't receive involvement
• Muscle stretches happens from contraction and Inhibition happens from golgi tendon reflexing
• The vestibul-ocular helps to stabilize The crossed extensor assists the individual if falling

Introduction to Senses

• A sensor responds sensing direct physical stimulation
• General senses are for awareness, vibration, proprioception, pain, pressure, as well as touch
• Special senses are for balance, as well as hearing

Sensory Processing Pathway

• The Stimulus happens such as light, touch, sound, and etc.
• The Sensor happens such as eye, receptor for the skin, and ear
• Next, the coordinator stimulates the nervous system for interpretation Muscle and glands respond from the stimulation A response from a movement, with sensation

Vision

• The process is that an eye has the pupil to regulate light, through the light passes with the cornea with processing that requires the retina
• The retina has rods plus cons and low/motion light as well as color sharpness
• Visual cortex perceives those images

Conditions

• The focusing of the vision transpires at the front, or behind, with nearsightedness, as well as farsightedness
• Presbyopia handles the reduction of the flexibility Cornea distorts vision

Hearing

• The sound is a mechanical oscillation in air pressure The loudness is on a high scale from amplitude, as the pitch is compared from high to low on the wave frequency that occurs
• The waves happen from the eardrum stimulating with sound and vibrating from the ossicles that connect to and stimulate the cochlea to vibrate in electrical signals which travel to the cortex for recognition

Balance

• Balance transpires with the vestibular actions
• Detects head movement with semi circle canals
• Eye reflex during movement stabilizes vision Body placement is corrected with the righting reflex

Smell

Molecules from air connect with cavity receptors that travel via bulb stimulation

• Can perceive up to 10,000 plus smells

Taste

Gustatory senses taste, such as salty, savory, bitter, sour, as well as sweet

• Water receptors hydrate with taste

Taste vs. Flavor

• Detection occurs chemically with the tongue Flavor combines with smells, sensation, temp, plus texture

Takeaways Key

• These are just general with pain, from sense receptor from the sense of touch to stimuli They depend on recognition via specific routes Vision has direct correlation to taste

Disorders of the Senses

Disorders transpire from receptors being lost, damaged, as well as reduced from the senses

Olfaction

• Sensory decline or damage to receptors from infections or damage is involved

Gustatory

• Taste sensation diminishes and olfactory functions malfunction

Vision

• Senile causes lens to be translucent or less elastic, or that aging causes hyperopia

Equilibrium/Balance

• Vertigo has issues with balance/spinning/dizziness or that triggers like drugs or motion are involved

Hearing

• Loud nose exposure causes hearing loss from middle ear plus cochlea damage

Vascular

• Strokes can happen from being lacunar, embolic, or thrombotic
• A "mini stroke", or TAI will occur with stroke risk indication
• • Hemorrhagic stroke occurs when there is bleeding in the brain and Subdural Hematoma occur
• • Vascular malformations or aneurysms that can cause damage to the organ

Infectious Disorders

• Meningitis (Inflammation of the Meninges) is the severe, life-threatening (Streptococcus pneumoniae, Neisseria meningitidis).
  • Fungal: Seen in those with immunocompromised issues Encephalitis (Brain Inflammation) occurs if the viruses are autoimmune or if it's West Nile
• Epidermal Abscesses from staph aureus causes compressions or pus collection in the spinal cord - back pain, fever, and or some paralysis

Neurodegenerative

• Alzheimer's from plaque or tangle issues can degrade or progress the mind/body with treatment not usually curing issues

Huntington or Parkinson's

-Huntington has movements that are not smooth or controlled with mood disturbances and are treated with movements with not a direct cure

• Parkinson's has more manageable symptoms but symptoms transpire from being dopamine deficient in substance nigra
• ALS has limited to no recovery or manageable action because motor neuron degrade
• Frontontemporal issues are unmanageable and lead to aphasia due to FTD

Keys to Remember

Problems transpire usually from the special hearing areas of the special body components Vascular occurs mostly with ischemia or hemorrhage damage

Endocrine System Overview

• The body functions depend on the secretion of hormones to regulate system actions Pituitary, pineal, gonads. hypothalamus, parathyroid, adrenal, hormone regulators and thyroid gland

Hormones Role

• They regulate all forms of reproduction, metabolism, immune response, homeostatic balance, and proper body formation Types come in two different formats

Hormones Types

• Steroidal - can pass through membranes, the cells respond via genetics, and Testosterone/Estrogen are the examples and have some lipids
• Hormones Non Steroidal - which cannot pass via membrane, use a second messenger or cyclic AMP and an example that requires this is Insulin

Pituitary Gland

• Location: base of the brain, connected to the hypothalamus via the infundibulum The two hormones function in pituitary

Hormones Posterior Pituitary

• These release ADH plus oxytocin (ADH in females and oxytocin for females only) made by hypothalamus and are stored

Hormones Anterior Pituitary

These function: FSH/GH/TSH/LH and ACTH - they release and produce for the body

Hormones Regulation

The negative feedback loop will respond and rise only unless if inhibited. so high responses signal to lower production The stimulation depends on hormonal, neural, and humoral stimuli to occur or be sent from the respective production organ. Neural corresponds to the stress, the hormone corresponds to the pituitary , plus the humor from the blood

Key Reminders

• The functions and actions of hormone balance is regulated and controlled due to pituitary.
• The hormones produce, send, as well as store. mostly anterior hormones Balance via homeostasis, reproduction, and mostly a negative feedback loop

Thyroid notes

The neck close/below to adams has key functions to maintain growth from skeleton, reproduction, to nervous system. increase blood pressure. and increase heat/metabolism

• T4 and T3 assists with that metabolism action and TSH stimulates the anterior body and is controlled via feedback
• The opposite occurs too from PTH which produces calcium
• Calcintonin cells of the C cell reduces blood supply by bone destruction and takes calium up too

Parathyroid notes

Small glands in bone from PTh releases calcium, this stimulate bone destruction.

• The essential is not only the nerve impulses, but contraction or also bloods response but also release.

Pineal notes

• Thalmus deep has main hormone, melatonin
• The time in the day is determined with cycle and highest has sleep that has highest to midday.
• Light via Thalmus controls

Adrenal Notes

Kidneys on above is medulla on inner side for the nervous and adrenal out side Mostly epinephrine.

• Increases alerts plus increases rates fight or flight

Adrenal cortex

• 3 layers from production of zone production that stimulates for blood glucose, sodium/balance, to DHEA production

Pancreas

• Enzymes in intestine exist to regulate digestive function and enzymes.
• Alpha cell increases glucose supply

Beta cell

• Decreases because cell absorbs more blood than before, and promotes fat because fat burns and produces energy while the body produces less storage trigger

Functions

• Ovaries help with estrogen and progesterone
• testosterone helps testes
• The placenta makes organs or secretes for hormones

Notes of Kidneys

• Production via erythropoietin occurs
• Renin is also blood regulation

Heart

ANP reduces as the pressure gets higher

Additional Fat and Bones

• Fat regulates hormones plus appetite. -Bones also require metabolism and insulin production Key Actions to Ponder
• The hormones and organ glands
• The calcium versus thyroid regulation Those regulate the the hormones and glands by body

Explore the nervous system, the body's communication network that uses electrical signals. Learn about the central and peripheral systems, including motor divisions. Discover the roles of afferent and efferent neurons in transmitting sensory and motor information.