The Anatomy of the Brain and Spinal Cord | The Central Nervous System PDF

Preview

Summary

The Nervous System
Protection of the Central Nervous System
Anatomy of Parasympathetic Division
Anatomy of Sympathetic Division
Anatomy of the Eye
Internal Structures
Static and Dynamic Equilibrium
Special Senses...

Description

The Nervous System

THE NERVOUS SYSTEM The Anatomy of the Brain and Spinal Cord | The Central Nervous System

Central Nervous System (CNS) Consists of the brain and spinal cord Functional Anatomy of the Brain The brain being the largest mass of the human body has 4 regions: I. Cerebral hemispheres or Cerebrum ● Cerebral hemispheres are paired (left and right) superior parts of the brain ○ Includes more than half of the brain’s mass ○ Its surface is made of ridges (gyri) and grooves (sulci) ○ Fissures are deeper grooves ○ Lobes are named for the cranial bones that lie over them ● 3 main regions of Cerebral hemispheres 1. Cortex - superficial gray matter 2. White matter - myelinated (enclosed in a myelin sheath) 3. Basal nuclei - deep pockets of gray matter

Basal Nuclei ● “Islands” of gray matter buried deep within the white matter of the Cerebrum ● Regulates voluntary motor activities by modifying instructions sent to skeleta cortex ● They help in bodily responses

●

Development and regions of the human brain

- with primary somatic sensory cortex/general sensory area which are loc fissure - there are two important area for speech: Broca’s Area & Wernicke’s Area * any damage in the Broca’s Area would prevent you from talking

Note: The neurons, being an amitotic cell, cannot reproduce, replicate, or regenerate when it’s been damaged… that’s why the different parts/lobes of the brain have overlapping functions.

3. Occipital Lobe - visual area of the brain 4. Temporal Lobe - olfactory and auditory center - involved in memory - it is referred to as the “psychic cortex ” since it is for abstract thinking as well

Notice that in the head region, t motor map since there are a lot lo (facial expression, chewing, tal there are lesser sensory neuron

II. Diencephalon ● Sits on top of the brain stem ● Enclosed by the Cerebral hemispheres ● Made of three structures: 1. Thalamus 2. Hypothalamus 3. Epithalamus

Thalamus ● Encloses the third ventricle

● ●

H

Relay station for sensory impulses passing upward to the Cerebral cortex Transfers impulses to the correct part of the cortex for localization and interpret

th h l

○

CSF is important as it cushions and protects the brain and spinal cord

III. Brain Stem ● Attaches to the spinal cord (connects the cerebrum to the spinal cord) ● Parts of the brain stem 1. Midbrain - Smallest portion of the brain stem - Dorsally located to that area are the four colliculi/corpora quadrigemina (hearin balance) - Auditory and visual reflex center - Anteriorly located will be the cerebral peduncles (little feet) for impulse transmis - With a black mass known as substantia nigra which regulates the general body movements

2. Pons - “Bridge” because it connects the cerebellum and cerebrum - Located above the medulla oblongata - Regulates breathing, chewing, swallowing, salivation, and balance Pyramids Pyramids-- prominent enlargements anterior to the medulla. It is involved skeletal muscles 3. Medulla oblongata - Most inferior part of the brain stem that merges into the spinal cord - Contains important centers that control: ○ Heart rate ○ Blood pressure ○ Breathing ○ Swallowing ○ Vomiting ●

Brain Stem: Reticular formation ○ Diffuse mass of gray matter along the brain stem ○ Responsible for cyclical motor functions (walking, chewing) and control over the interna ○ It will soon be forming the reticular activating system (RAS), which: ■ plays a role in awake/sleep cycles and consciousness ■ filter for incoming sensory information ■ Any damage to the RAS can cause comatose

IV. Cerebellum (little brain) ● Cauliflower-like mass with gyri (elevations) and sulci (grooves). It function for balance, muscle coordinated movement and learning a motor skill (e.g. playing a piano) ● Alcohol has an effect on this area ● Any damage to this area would result to ataxia, clumsy drunken-like movement

Function of Major Brain Regions

Protection of the Central Nervous System 1. Meninges ● Dura mater (Dura=hard; hence, hard matter) ○ Outermost leathery layer ○ Double-layered external covering ■ Periosteum - connective tissue attached to inner surface of the skull ■ Meningeal layer - outer covering of the brain ○ Folds inward in several areas ■ Falx cerebri ■ Tentorium cerebelli - extension of the dura mater

●

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

●

Pia Mater ○ Internal later ○ Clings to the surface of the brain and spinal cord

2. Cerebrospinal fluid (CSF) ● Similar to blood plasma in composition ● 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 ● Any blockage to the passageway will cause hydrocephalus in babies

Functional Anatomy of the Spinal Cord ● Extends from the foramen magnum of the skull to the first or second lumbar vertebra ○ Foramen magnum - found in the posterior portion of the skull ● Cauda equina is a collection of spinal nerves at the inferior end ● Provides a two-way conduction pathway to and from the brain ● 31 pairs of spinal nerves arise from the spinal cord ● Consist of a central mass of gray matter and a peripheral array of white matter ○ Gray matter - looks like a butterfly or letter “H” a.) Dorsal/Posterior horns - consist of the central processes of sensory and association neurons that enters b.) Ventral/Anterior horns - Two anterior projections with cell bodies of motor and association neurons that - together, the dorsal and ventral root, will form the spinal nerves - Damaged to the ventral root will result to flaccid paralysis, the impulses cannot cannot go out of the spinal cord - At the center is a Central Canal containing CSF ○

White matter - with myelinated fiber tracts; it is divided into columns/funiculi a.) Posterior column - Contains ascending tracts (sensory and afferent tracts) carrying input/impulses to the brain b.) Lateral column - Contain both ascending and descending motor tracts carrying impulse from the brain to the skeletal muscles

THE NERVOUS SYSTEM ● master control and communication center of the body ● thoughts, emotions, and actions are all because of the nervous system’s activity ● instant reaction/immediate reaction = through the senses or rapid electrical impulse = very specific and caus 3 OVERLAPPING FUNCTION FUNCTIONS S (similar to feedback loop)

Recall: Feedback Loop A receptor receives sensory input which is sent to the brain/control center for integration or processing. Brain and determines the appropriate response/output. Later on, it will be sent back to create a motor response. 1. Sensory Input = sent to the brain for processing 2. Integrat Integration ion = determine appropriate response 3. Motor Output = response/action *These 3 functions enable the nervous system to create a rapid/fast response. ● It uses sensory receptors to monitor changes both inside and outside the body, called stimuli. ●

STIMULI ● When these changes in the body or stimuli are detected, the gathered info (sensory input) will be sent to the processes and interprets sensory input) then, it will send back its response through electrical impulses = mu (motor output). ORGANIZATION OF THE NER NERVOUS VOUS SYSTEM *The nervous system acts as a coordinated unit. It functions both structurally & functionally.

STRUCTURAL ● Central Nervous System (CNS) ● Peripheral Nervous System (PNS)

CENTRAL NERVOUS SYSTEM (CNS) ●

Organs ○ Brain

●

○ Spinal Cord ○ found in the dorsal cavity of the body Function

● ● ●

Activities of the nervous system Concerns only the PNS = Sensory & Motor Division Nerves only

SENSORY/AFFERENT DIVISION (to go towards) ● ● ●

Nerve fibers that carry information or convey impulses towards brain/spinal cord (CNS) Impulses that came from sensory receptors located from the various parts of the body Keeps the CNS constantly informed of what’s happening inside & outside the body ○ Somatic sensory (afferent) fibers - skin, joints, and skeletal muscles ○ Visceral sensory (afferent) fibers - visceral organs

MOTOR/EFFERENT DIVISION (away from) ● ●

Nerves fibers that carry impulses away from CNS organs to effector organs (muscles and glan Activates the muscles/glands or effect a motor response

SOMATIC NERVOUS SYSTEM = VOLUNTARY ● ●

Consciously (voluntarily) controls the skeletal muscles Not all skeletal muscles are controlled by somatic nervous system (ex. muscle reflexes

AUTONOMIC NERVOUS SYSTEM = INVOLUNTARY ● ● ●

Regulates events that are automatic or something that we can’t control Automatically controls smooth and cardiac muscles & glands (ex. Activities of the cardia of glands, and Pagkalam ng tyan) Divided into 2: ○ Sympathetic (stimulates/activates flight or fight) ○ Parasympathetic (inhibits/restores the body to a state of calm)

NERVOUS TI TISSUES: SSUES: STRUCTURE AND FUNCTIO FUNCTION N ● Nervous tissue is made up of two principal cell types ○ Supporting Cells (called neuroglia, glial cells, or glia) ■ Supports neurons ■ Resembles neurons structurally because they also contain cell extensions or processes ■ Yet, are unable to transmit/conduct nerve impulses ■ never lose the ability to divide ○ Neurons ■ Do not divide or do not undergo cell division ■ Brain tumors/Gliomas = tumors (product of irregularities from cell division) formed by neurogl ■ Highly specialized cells ■ Can transmit messages from one part of the body to another NERVE TISSUE: SUPPORT CE CELLS LLS ● Support cells in the CNS lumped/grouped together as neuroglia (nerve glue) ● General functions ○ Support ○ Insulate ○ Protect neurons CNS GLIAL CELLS (only in CNS)

ASTROCYTES ● ● ● ● ●

Abundant, star-shaped cells Brace and anchor neurons to blood capillaries Determine permeability and exchanges between blood capillaries and neurons Protect neurons from harmful substances in blood Control the chemical environment of the brain - mop up or clean up link potassium ions which could play a major role in generating nerve

impulses; recapture chemicals used for communication

EPENDYMAL CELLS ● ●

Line cavities of the brain & spinal cord Cilia (hairlike protrusions) assists with the circulation of the Cerebrospinal Fluid (forms a protective layer or watery cushion in the brain & spinal cord for protection)

OLIGODENDROCYTES ● ● ●

Wrap around nerve fibers in the CNS Produce myelin sheaths in the neurons found in CNS Counterpart in PNS = Schwann cells

PNS GLIAL CELLS

SCHWANN CELLS ●

Form myelin sheath around nerve fibers in the PNS

SATELLITE CELLS ●

Protect and cushion neuron cell bodies

NERVOUS TISSUE: NEURON NEURONS S *Neurons differ structurally from each other, others have more processes than the rest and vice versa yet, they still ha NERVE CELLS ● Cells specialized to transmit messages (nerve impulses) ● Major regions of all neurons ○ Cell body- nucleus (nucleus and organelles essential for the metabolism of the entire neuron) a ○ Processes- protrusion; extensions; fibers that extend from the cell body CELL BODY ● Metabolic center of the neuron ● Contains the transparent nucleus with a large nucleolus ○ Nissl Bodies ■ Rough endoplasmic reticulum ■ Surrounds cell body ○ Neurofibrils ■ Intermediate filaments that maintain cell shape ■ Provides stability *Cell body lacks centrioles (plays a huge role in mitosis; moves at the end of each poles that re chromosomes) thus, it can’t divide MITOCHONDRION ● Gives energy to the cell body to perform its function PROCESSES (fibers)

● ●

Extensions/structures that extend from the cell body Vary in length from microscopic to about 7 feet ○ DENDRITES

MYELIN ● White, fatty material covering axons ● Protects and insulates fibers ● Speeds nerve impulse transmission ● Just like a wire in an electrical cord, it keeps the electricity along a desired path; Myelin ensures the co in fibers ● Disorder = Multiple Sclerosis (myelin sheath hardens and turns into scleroses, with that nerve impulse back; naiiba ang path; hindi nararating ng nerve impulse ang supposed target) ○ Multiple Sclerosis is an autoimmune disorder - own immune system attacks the cells, thinkin no cure ○ Patients with this disease are injected with interferons - a hormone like substance that lesse immune system from attacking the myelin sheaths so that it won’t solidify much further MYELIN SHEATHS ● Schwann Cells ○ Wrap axons in a jelly roll-like fashion (PNS) to form myelin sheath ○ Axons located outside the CNS are myelinated or surrounded by schwann cells ■ Neurilemma ● Part of the Schwann cell external to the myelin sheath ● Another layer above myelin sheath for added protection ● During damage in the peripheral nerve, neurilemma remains intact thus, the fibe ■ Nodes of Ranvier ● Gaps in the myelin sheath along the axon ● OLIGODENDROCYTES ○ Produce myelin sheath around axons of the CNS ○ Unlike schwann cells na need ng marami, kahit isa lang na oligodendrocytes, kaya niya mag s the same time ○ Lacks a neurilemma thus, no additional protection; can’t regenerate if damaged; grave effect

*Wrapping processes of Schwann cells -The membrane is loose but the schwann cell cytoplasm is gradually squeezed from between the membrane layer. So when the wrapping process is done, a tight call of wrapped membrane/myelin sheath enclose the axon. TERMINOLOGIES NUCLEI - clusters of cell bodies in the CNS GANGLIA - collections of cell bodies outside the CNS in the PNS TRACTS - bundles of nerve fibers in the CNS NERVES - bundles of nerve fibers in the PNS WHITE MATTER - collections of myelinated fibers (tracts) GRAY MATTER - mostly unmyelinated fibers and cell bodies

●

Functional Classification ○ Sensory (afferent) neurons

RECEPTORS PRESENT IN TH THE E SKIN

A. B. C. D. E.

Free nerve endings (pain and temperature receptors) Meissner’s corpuscle (touch receptor) Lamellar corpuscle (deep pressure receptor) Golgi tendon organ (proprioceptor) Muscle Spindle (proprioceptor)

○

Motor (efferent) neurons ■ ■

○

Carry impulses from CNS to the viscera and/or muscles and glands (effector organs) Cell bodies of motor neurons are usually located in the CNS

Interneurons (association neurons)

■ Cell bodies located in CNS ■ Connect sensory & motor neurons ■ Completes the communication pathway *Motor/Efferent Neurons transmits impulses from CNS to the effectors in the body

○ ○ ○ ○

Single process which is very short and divides immediately into distal and proximal process small branches at the end of the remainder of the peripheral process and the central process function Axon conducts nerve impulses both towards and away from the cell body Ex. Sensory neurons found in PNS

NERVE IMPULSES: TRANSM TRANSMISSION ISSION OF THE SIGNAL AT SY SYNAPSES NAPSES ● Electrical conditions of a resting neuron’s membrane ○ The plasma membrane at rest is inactive (polarized) ○ Fewer positive ions are inside the neuron's plasma membrane than outside ■ K+ is the major positive ion inside the cell ■ Na+ is the major positive ion outside the cell ○ As long as the inside of the membrane is more negative (fewer positive ions) than the outside, the cell

*Recall: Sodium-Potassium Pump and the Sliding Filament Theory *Video Links: https://www.youtube.com/watch?v=XnksofQN8_s https://www.youtube.com/watch?v=WhowH0kb7n0

● ● ● ●

Reflexes are rapid, predictable, and involuntary responses to stimuli Reflexes are pre-programmed response to a given stimulus Reflexes occur over neural pathways called reflex arc Two types of reflexes: ○ Somatic Reflexes ■ Reflexes that stimulate the skeletal muscles ■ Involuntary, although skeletal muscles is normally under voluntary control ■ Ex. pulling your hand away from a hot object ○ Autonomic Reflexes ■ Regulate the activity of smooth muscles, the heart, and glands ■ Movements that you can’t control; involuntary ■ Ex. regulation of smooth muscles, heart and blood pressure, glands, digestive system ■ Examples of involuntary reflex: salivary reflex, pupillary reflex

FIVE BASIC ELEMENTS OF A R REFLEX EFLEX ARC 1. Receptor - reacts to the stimulus 2. Effector - eventually stimulated, can either be a muscle or gland 3 & 4. Sensory and Motor Neurons - connects the receptor and effector with each other 5. Central Nervous System (brain and spinal cord) - contains the interneurons between the sensory and motor ne

TWO TWO--NEURON REFLEX ARC ● Patellar or knee jerk reflex ● During physical exam to determine the general health of the motor portion of our nervous system

*Spine Reflex - reflexes usually involve the spinal cord neurons and it happens without the brain development; as long as the spinal cord is functional the spinal reflexes will work *Other reflexes requires the brain to help because there are many different types of information that are needed to b response Ex. pupillary response to the light *Exaggerated/distorted reflexes, no reflex at all, and twitching are nervous system disorders THE NERVOUS SYSTEM

The Peripheral Nervous System Organization of the Nervous System The Peripheral Nervous System A network of nerves spread across our body Structure of a Nerve ● Nerves are bundles of neurons found outside the CNS ● Endoneurium is a connective tissue sheath that surrounds each fiber ● Perineurium wraps groups of fibers bound into a fascicle ● Epineurium binds groups of fascicles ● Mixed nerves - contain both sensory and motor fibers ● Sensory (afferent) nerves - carry impulses towards the CNS ● Motor (efferent) nerves - carry impulses away from the CNS The Peripheral Nervous System is consist of 43 pairs of nerves ● Cranial Nerves

○

12 pairs of nerves serve mostly the head and neck ■ All Cranial Nerves are paired, meaning they appear on both sides of the brain

l

■

Ventral Rami (EXCEPT T1 to T12) - form a complex of networks (plexus) for the anterior Plexus ● Networks of nerves serving motor and sensory needs of the limbs ● Form from ventral rami of spinal nerves in the cervical, lumbar, and sacral regions ● There are 4 Plexuses: 1. Cervical 2. Brachial 3. Lumbar 4. Sacral

Somatic Nervous System ● ●

Motor neuron cell bodies originate inside the CNS Axons extend to skeletal muscles that are served

Autonomic Nervo ●

●

●

Motor subdivisions of the PNS ○ Consists only of motor n ○ Controls the body autom the “involuntary nervous ○ Regulates cardiac and sm Chain of 2 motor neurons ○ Preganglionic Neuron - in ○ Ganglionic Neuron - exte Has 2 arms ○ Sympathetic division - m extreme situations (e.g. F ○ Parasympathetic division

Anatomy of Parasympathetic Division ● ●

●

Parasympathetic Division is also known as the craniosacral division Preganglionic neurons originate in: ○ Cranial nerves III, VII, IX, and X ○ S2 through S4 regions of the spinal cord Preganglionic neurons synapse with terminal ganglia; from there, postganglionic axons extend to organs that s

Anatomy of Sympathetic Division

● ●

Sympathetic Division is also known as the thoracolumbar division Preganglionic neurons originate from T1 through L2 ○ Axons pass through a ramus communicans to enter a sympathetic trunk ganglion S th ti t k...