Nervous System: Neurons and Classification

• Neurology studies the nervous system
• The nervous system processes internal and external environmental changes, regulating appropriate bodily functions in response

Nervous System Details

• The neuron is the functional unit
• A neuron consists of an axon, dendrites/dendrons, and a cell body
• Axons carry impulses away from the cell body
• Dendrites/dendrons carry impulses toward the cell body
• The cell body contains a nucleus, neuroplasm, neurofibrils, Nissl bodies, mitochondria, Golgi apparatus, ER, ribosomes, inclusions, neurosecretory materials, and a cell membrane

Neuron Classification

By Number of Processes

• Apolar neurons have no processes
• Unipolar neurons have one process
• Bipolar neurons have two processes
• Pseudo-unipolar neurons are a subtype
• Multipolar neurons have multiple processes

By Relative Lengths

• Golgi type-I neurons have short, numerous dendrites and long axons, found in peripheral locations
• Golgi type-II neurons have short axons, morphologically similar to dendrites, confined to gray matter for synaptic connections
• Amacrine neurons, unique to the retina, contain terminal fibers of axons and dendrons but lack axons

The Nervous System

• The central nervous system (CNS) is the body's master control unit
• The peripheral nervous system (PNS) links the body to the outside world
• The CNS includes the spinal cord and brainstem
• The brainstem connects the brain to the spinal cord
• The brain is divided into the hindbrain, midbrain, and forebrain
• The PNS consists of the autonomic and somatic nervous systems
• The autonomic NS regulates involuntary bodily processes
• The autonomic NS includes functions like regulating heart rate, respiration, digestion, and pupil contraction, operating automatically without conscious direction
• The somatic NS carries sensory information to the CNS, relays motor commands to muscles, and controls voluntary movements
• The craniospinal NS consists of the cranial and spinal nerves
• The sympathetic NS prepares the body for action and stress ("fight or flight")
• The parasympathetic NS calms the body and helps conserve energy

Brain Meninges

• Meninges are protective membranes surrounding the brain and spinal cord, providing structural integrity, cushioning, and infection defense
• Cerebrospinal fluid (CSF) are present in the brain
• From outermost to innermost the meninges layers are: dura mater, arachnoid mater, and pia mater

Dura Mater

• The dura mater is the toughest and outermost meningeal layer
• Made of dense, fibrous connective tissue which gives mechanical protection to the brain
• Has two layers: periosteal and meningeal
• The periosteal layer attaches to the inner surface of the skull
• The meningeal layer is closer to the brain and continuous with the dura mater of the spinal cord
• Structures formed include: falx cerebri, tentorium cerebelli, venous sinuses, and diaphragm sellae

Arachnoid Mater

• The arachnoid mater is a thin, web-like membrane located beneath the dura mater
• Has a spiderweb-like appearance due to delicate fibers that extend downwards
• The subarachnoid space beneath it is filled with CSF
• Arachnoid villi or granulations protrude into dural venous sinuses and allow CSF to drain into the bloodstream

Pia Mater

• The pia mater is the thinnest and innermost layer, attached directly to the brain's and spinal cord's surface
• Closely follows brain contours including sulci and gyri
• Contains rich vascularization to provide oxygen and nutrients

Meningeal Spaces

• The epidural space is located between the skull and dura mater (in the spinal cord)
• Contains fat and blood vessels
• The subdural space lies between the dura and arachnoid mater
• A potential space that may fill with fluid or blood during trauma
• The subarachnoid space is between the arachnoid and pia mater
• Filled with CSF, which cushions the brain and spinal cord from mechanical shocks
• Houses blood vessels that supply the brain

Cerebrospinal Fluid (CSF)

• CSF is a clear, colorless fluid surrounding the brain and spinal cord
• CSF is produced primarily by the choroid plexus via capillaries located in the brain ventricles
• Ependymal cells of the choroid plexus secrete CSF through active filtration of blood plasma

Brain Ventricles

• The brain consists of network of cavities filled with cerebrospinal fluid (CSF)

CSF Flow

• CSF forms in the lateral ventricle
• The CSF flows through the foramen of Monro
• It then progresses to aqueductus Sylvius
• CSF then goes from the third ventricle to the fourth ventricle
• CSF flows through the foramen of Magendie and foramen of Luschka
• Then proceeds through the cisterna magna and cisterna lateralis
• The fluid flows through central canal
• CSF moves to Subarachnoid spaces
• The CSF then passes through the cerebral hemispheres and spinal cord

Brain Embryology

• During brain development, there are three primary vesicles
• The primary brain vesicles are the prosencephalon (forebrain), mesencephalon (midbrain) and rhombencephalon (hindbrain)

Brain Morphology

• Brains are irregularly shaped vs. the regular shape of the spinal cord
• Brain size does not correspond to animal size
• Average brain weighs:
• 500 grams in ox
• 1.5 kg in humans
• 750 grams in horse
• 60 grams in dog

Brain Terminologies

• Nuclei are clusters of neuron cell bodies located deep within the brain or spinal cord
• Ganglia are collections of neuron cell bodies outside the central nervous system, in the peripheral nervous system (PNS)
• Tracts are bundles of axons (nerve fibers) within the central nervous system
• Nerves are bundles of axons (nerve fibers) inside the peripheral nervous system
• Commissures are bundles of nerve fibers connecting corresponding regions of the left and right hemispheres, enabling communication

Brain Views

• The cerebral hemisphere and cerebellum are visible from a dorsal view
• The medulla oblongata is partially visible
• Semi-ovoid cerebral hemispheres are bisected by a deep longitudinal fissure and separated from the cerebellum by a transverse fissure
• Ridges (gyri) and grooves (sulci) create a distinct pattern on each hemisphere
• Caudal parts, medulla oblongata, pons, and midbrain are visible in Ventral Views
• The forebrain, including the hypothalamus, is part of the cranial section
• The crossing/chiasm formed by the optic nerve, and round piriform lobes are also part of the cranial section
• Superficial origins of all cranial nerves except the trochlear are visible

Brain Matter

• Gray matter contains neuron cell bodies, dendrites, and unmyelinated axons
• Gray matter mainly integrates information and processes
• Gray matter is found in butterfly shaped structures in the inner spinal region
• Gray matter is slower at signal transmission
• White matter contains myelinated axons (nerve fibers)
• White matter transmits signals
• White matter lies beneath the gray matter

Brain Sections

• The Brain is split into: Forebrain, Midbrain and Hindbrain
• The Forebrain splits into: Diencephalon and Telecephalon
• Diencephalon contains: epithalamus, thalamus, metathalamus, & hypothalamus
• Telecephalon contains: cerebral hemispheres
• Midbrain components is mesencephalon
• Hindbrain contains: myelencephalon and metencephalon
• Myelencephalon: medulla oblongata
• Metencephalon: pons and cerebellum

The Forebrain

• Split into two main parts :
  • Diencephalon
  • Telecephalon
• In Diencephalon, following components are present :
  • Epithalamus
  • Thalamus
  • Sub thalamus (dorsal)
  • Metathalamus
  • Hypothalamus
• Following part present in Telecephalon :hemispheres

Epithalamus

• Main portion of the epithalamus is the pineal gland.
• Contains a small ovoid gland, positioned dorsally between thalami and corpora quadrigemina.
• Positioned in posterosuperior the third Ventricle
• Hollow cavity which is a small recess of the Third ventricle
• The gland helps regulate behavior, and ovarian activity in animals(sheep, horse).

Thalamus

• Largest portion of the Diencephalon
• Positioned in the the walls of the 3rd ventricle
• Dorsal thalamus is composed of a large number of nuclei
• Subthalamus is a continuation of mesencephalon.

Hypothalamus

• Makes floor and walls up of 3rd Ventricle
• Optic chiasm is present in the front, near the optic nerves
• Near the mammillary body, which is connected to the the pituitary glands

Metathalamus

• Consists of lateral and medial bodies. Lateral geniculate body: receives fibers from optic tract
• Medial geniculate body: Relays acoustic signals to the cortex

Telecephalon

• Main component is Hemisphere
• Hemisphere Structure Information:
  • The largest portion is the brain with symmetrical halves.
  • It is connected by commisural fibers.
  • The corpus callosum, and spreads radial in the white matter
  • Has high concentration of cerebral cortex matters
    • Has underlying white matter
    • Holds accumulations of base Nuclei

Pallium/ Cerebral cortex/ Surface grey matter:

The pallium components include three sections, as divided up by matter:

1. Paleopallium is limited to the brains base
2. Neopallium: Large portion of telencephalon contains high concentration of gyri and sulci
3. Archipallium contains the hippocampus.

Rhinencephalon

• Encompasses the olfactory bulb, tract, and striae, trigonium olfactorium, and piriform lobe
• Structures elongate and curve upwards in front of the frontal pole
• Olfactory Bulbs : The convex exterior is fit into the ethmoid fossa
• Olfactory Tracts: Have wide range of white matter
• The nerves are contained on the lateral cavities.
• The two types of Olfactory Striae:
  • Lateral: larger than medial
  • Medial both join at the piriform lobe

Limbic system/Visceral brain:

• Controls emotional stimuli
• Contains olfactory and piriform lobes
• Houses the hypothalmus.
• Amygdaloid Structure:
  • Almond shaped, concentrated near the base.
• The hippocampus works as a memory center by transfer of cerebral cortex
• Balances emotion along the cerebral cortex The limbic system is also concerned with emotion, behavior, endocrine and somatic functions

Midbrain

• Contains three layers: dorsal, middle, ventral crura/cerebral peduncles.

• Midbrain Structures include : the forebrain, midbrain, and hindbrain .

• The dorsal tectum consists of paired rostral and caudal swelliings called colliculi.

• Caudal/ inferior colliculi relays center called the auditiory pathway

• Midbrain contains the mesencephalic/cerebal part of 3rd and fourth ventricles

Cerebral Crura Two-fold Structure

• Two main peduncles make up for the structure and connect to the spiral
• Consists of ascending and descending pieces of spiral cord.
• The tuber is the hollow with tuber cinerum
• Covered by mammillary body/corpus albicans

Substantia Nigra

• Contains an abundance of pigmented cells
• Has a large concentration of the midbrain

Hindbrain

• The Hind brain is a large mass spanning from the pons to the medulla and cerebullem
• Medulla oblongata, continuation of spinal cord and extends from the foramen magnum to caudal margin of pons
• Ventral surface: marked by median fissure, continues with that of spinal cord, flanked by longitudinal ridges c/a pyramids

Trapezoid body/ Pyramidal decussation Functions

• Consists of ascending.descsnding fibers and the 5-12th craneal nerves.
• Regulates the heart, respiration and regulation of body temperature

POONS - Nuclei Structure Information

• Consists of Nuclei, affects coordination ,cerebellum controlled by vitals and repiration
• Contains a trgeminal nerve from the frontal lobe
• Located beetween the mo the mb
• Contain trnsverse grooves

The Cerrebelum Structures

• Located in the middle of the poons to medulla, covers 3 lobes, anterior posterrior

• Each lobe contains longitudinal fissure

• Center zone is called vermis

• Outer zone ir irregular

• Surface of the brain stem is covered by multiple curves and curves of fold and folia.

• The tissue gives tertiary laminae which look like arbors = arborvitae/ tree of life.

Cerebellum Three Pundicules

Structures:

1. Superior: connects cerrebelum with mind brain
2. Middle: comes from the spons 4, Inferier comes from MO to cerebrum Functions Controls posture and stabiility receives inputs from auditirory and visual systems Cerebellum has three peduncles

Spinal Cord Structure Information

• a medulla spinalis
• Protected via cns Located near the vertebral collumn Cylindricaly divided into two halves with dorsal and longitudinal fissurers. Cranial end Continuous with the medulla, around foramen magnum.
• Has a caudial end in many parts mostly near domestic vertebrae to the middle sacrum. Spinal cord is divided into cervical thoracic lumsacral and coccygeal.

Spinal cord structure

• Divided into cervical, thoracic, lumbar, sacral and coccygeal

    - Spinal  consists of gray Matter(inner), and outer matter (outer Part)
  
    -Has dorsal/vetral root forming spinal
  

• Functions, composed of Neuronal synapse

  . The spinal cord also composed of motor trats.

Spinal cord composition

• Divided in thee sets/horns, with Gray Matter

Spinal matter is devided into thrree horns

• Contains sensory that reeive the sensory