2023_04_05_02_26__BIOL 2401 Lecture Chapter - 11-14 (2)_recording 1_a571d79a-1a68-48dd-9e3b-36912610ecd4_recording

Organization of the Nervous System

• The nervous system is divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

Central Nervous System (CNS)

• Composed of the brain and spinal cord only.

Peripheral Nervous System (PNS)

• Includes everything else in the nervous system besides the brain and spinal cord.

• Consists of:

  • Cranial nerves: 12 pairs of nerves from the brain.

  • Spinal nerves: 31 pairs of nerves from the spinal cord.

  • Branches of these nerves reaching every part of the body.

• Acts as an interface between the body and the CNS.

  • Facilitates the collection of information from the body to the CNS and the relay of signals from the CNS to the body.

Cranial and Spinal Nerves

• Cranial nerves emerge from the brain, while spinal nerves emerge from the spinal cord.

• Brain anatomy includes structures such as cerebrum, diencephalon, thalamus, hypothalamus, medulla oblongata, pons, and midbrain.

Cells of the Nervous System

• Approximately 100 billion neurons, which receive and send information.

• Glial cells (neuroglial cells) support the function of the nervous system without directly participating in communication.

Meninges

• Membranes protecting the brain and spinal cord; there are three layers.

  • Dura mater: The outermost membrane.

  • Arachnoid membrane: The second membrane.

  • Pia mater: The third and innermost membrane.

• Each individual membrane is called a meninx.

Structure of Meninges and Spaces

• Spinal cord is protected by three membranes:

  • Dura mater (outermost layer).

  • Arachnoid mater/membrane (middle layer).

  • Pia mater (innermost layer): Intimately attached to the spinal cord.

• Similar arrangement around the brain with dura mater, arachnoid membrane, and pia mater.

• Meninges cover the entire CNS.

• Spaces associated with the meninges:

  • Subdural space: Between the dura mater and arachnoid membrane.

  • Subarachnoid space: Between the arachnoid membrane and pia mater.

  • Epidural space: Between the vertebrae and dura mater.

Meninges - Detailed Explanation

• Coverings made of membranes that protect the brain and spinal cord.

• Three layers: dura mater, arachnoid membrane, and pia mater.

• Each layer is called a meninx (singular), and all layers together are called meninges (plural).

• Meningitis: Inflammation of the meninges.

Dura Mater

• Outermost membrane; tough and thick.

• Made of dense fibrous tissue, specifically white dense fibrous tissue, composed mostly of collagen fibers.

• Nerves and blood vessels pass through or around the dura mater.

• Sometimes referred to as the internal periosteum of the cranial bones.

• Extends within the poles of the brain to support brain tissue.

• Ends like a blind sac at the level of the second sacral vertebrae.

• Epidural space: Located between the vertebrae and dura mater.

  • Contains blood vessels, loose connective tissue (areolar tissue), and fatty (adipose) tissue.

Arachnoid Membrane

• Middle membrane; thinner and nonvascular compared to the dura mater.

• Located under the dura mater.

• Subdural space: Space between the dura mater and the arachnoid membrane; contains serous fluid.

  • Serous fluid reduces friction.

Pia Mater

• Thinnest and most delicate membrane.

• Intimately adheres to the surface of the brain tissue and spinal cord tissue.

• Subarachnoid space: Space between the arachnoid membrane and the pia mater.

  • Contains cerebrospinal fluid (CSF).

Brain Ventricles

• Spaces within the brain; there are four ventricles.

  • Lateral ventricles (left and right).

  • Third ventricle.

  • Fourth ventricle.

• Lateral ventricles connect to the third ventricle via the interventricular foramen.

• Third ventricle connects to the fourth ventricle via the cerebral aqueduct.

• CSF is produced inside the ventricles by a specialized blood capillary system called the choroid plexus.

• CSF circulates around the brain and spinal cord before being reabsorbed into the blood.

• CSF escapes through three holes (apertures) in the fourth ventricle: aperture of Lusca and aperture of Magendie.

• Functions of CSF:

  • Forms a watery cushion around the brain and spinal cord to protect them from concussion.

  • Supplies glucose to brain cells and spinal cord cells for energy.

  • Contains macrophages to fight infections in the nervous system.

  • Keeps the CNS hydrated and dilutes waste substances.

  • Contains ions to help maintain the CNS's chemistry and pH balance.

• The fluid is made from brain. Then is circulated around the brain and spinal cord. Then again absorbed into the blood.

Brain Ventricles Connections

• We have four ventricles in total.

• Lateral ventricle is connected to the the third ventrical by the interventricular foramen

• Third Ventricle and fourth ventricle are connected by means of a narrow channel called cerebral aqueduct

• Ependymal cells line the ventricle and helps in ciculation.

• Continuous creation of the fluid(CSF). Is at about 500 mls peraday.

  • We see only 140mls around brain and spinal cord.

Composition and Functions of CSF

• CSF contains water, proteins, salts, glucose, macrophages, and various ions.

• Functions of CSF:

  • Forms a pad around the CNS to protect it from shock.

  • Provides nutrition via glucose.

  • Helps the CNS maintain ionic balance (pH balance/acid-base balance).

  • Removes waste substances with water.

• It escapes through the subarachnoid space

• Fourth Ventricle has one hole on top and two on the sides.

  • Opening on the top the aperture of Magendie

  • Two on the side are aperture of Luska
    Central Canal is at the middle of spinal cord.

  • Fluid can also be found in the central canal.

Important Neural Components

White Matter vs. Gray Matter

• Gray matter: Areas with a high concentration of neuron cell bodies (soma) and dendrites.

• White matter: Areas with a high concentration of myelinated cell processes (axons).

• Brain has white matter Bulk of the brain.

• Surface of the bain is grey matter.

Nerve vs. Tract

• Nerve: A bundle of fibers (axons) in the PNS (outside the brain and spinal cord).

• Tract: A bundle of fibers (axons) in the CNS (inside the brain and spinal cord).

Ascending Tract vs. Descending Tract

• Ascending tract: Carries signals upward (e.g., from spinal cord to brain).

• Descending tract: Carries signals downward (e.g., from brain to spinal cord).
  Ascending carrysignals upward from spinal cord to brain.
  *Lower spinal cord to upper spinal cord.
  *Descending* carry signals download from the brain.
  *Upper spinal cord to lower spinal cord.

Ganglion vs. Nucleus

• Ganglion: A mass of neurons in the PNS (outside the CNS).

• Nucleus: A mass of neurons in the CNS (inside the CNS).

Column vs. Horn

• Column: Areas of white matter in the spinal cord.

• Horn: Areas of gray matter in the spinal cord.
  Horns are the extended park of grey matter, spinal cord.

Classification of Nerve Fibers

• Classification using somatic and afferent/efferent terms:

  • Somatic refers to voluntary functions (e.g., skeletal muscles).

  • Visceral refers to involuntary functions (e.g., smooth muscles).
    Afferent refering to incoming.
    Efferent referring to outgoing.

• A fibers: Large diameter, myelinated, fastest impulse speed (30 m/s).

• B fibers: Medium diameter, moderately myelinated, medium impulse speed (10 m/s).

• C fibers: Smallest diameter, unmyelinated, slowest impulse speed (0.5 m/s).

A fibers fastest, with larger diameter, plenty of myelin, Speed at a rate of 30 mts per second.

B fibers moderate, medium diameter, average myelin. At a Speed at a rate of 10 mts per second.

C fibers slow, unmyelinated, At a Speed at a rate of 0.5 mts per second.

Structure of the Human Brain

The brain is wavy
Gyrus the high areas
Sulcus the low areas

• Different Lobes made of different colors.*

The Cerebrum

• Cerebrral cortex is the grey matter that covers the brain.

• Structures: gyri (convolutions), sulci (grooves), lobes (frontal, parietal, temporal, occipital), cerebral cortex (gray matter), white matter, corpus callosum.

• Corpus Callosum connectes the two sides to communicate.*

• Function: higher brain functions (interpretation, reasoning, thought), sensory/motor/association areas.

• 90% left side of brain is dominant *

• Contralateral Control. Left of brain control right, vice versa.

The Cerebellum

• Small when compared to cerebrum.*

• Cerebellar hemispheres.

• Worm that connects the two side*

• Function: Coordinates muscle function and keeps Balance(Equilibrium).*

The Thalamus

• Thalamus is located in middle and inferior side of the brain.*

• Function: relay station for sensory information, interprets pain/pressure/touch/temperature/light, memory, motion.
  Thalamus Huge Memory center.

The Hypothalamus

• Function: hypothalamus helps to keeps blood temperature constant, keeps blood water concentration constant, Hormone constrationconstant.

• Small and has huge function.*

• Connected to pituitary gland.*

• Functions: monitors blood temperature/water concentration/hormone concentration, associated with pituitary function, produces hormones (endocrine system).
  Can produce Hormones.
  Thermometer.

The Midbrain

• Corpura quadrigemina

• four Masses of neurons, four nuclear, four masses of cells.

• Superior colliculi, and Inferior colliculi. Reflexes. Head, neck and eye movement.

• Substantia Nigra: the dark substance. For production dopamine. Important for contraction.
  Ocumotor nerve and trochlear nerve originate here.

The Pons

Help Breathing. Pneomotaxic area and Apneustic. It has Trigiminal, abducens Facial.

The Medulla Oblongata

• End brain right before the spinal cord starts.*
  Vestibular nuclear complex is in there.

• Has ascending and descending tracts, pyramidal degradation ( fibers crossing side). Has Vestibular nuclear complex. Helps breathing.
  Medulla helps co-ordinates. Pneumotoxic area and apneustic for breathing.

Structure of the Spinal Cord

• 1 and half feet long, Inside Cervical canal, Thoracic canal and Lumbar Canal.*

• 31 segments and each segment gives rise to a pair of Spinal nerves.

  • 8 Cervical nerves Pair.

  • 12 Throacic nerve Pair.

  • 5 Lumbar nerve Pair.

  • 5 Sacral nerve Pair.

  • 1 Occipital nerve Pair.
    Cervical enlargement helps supply UPPER part of the body coming out of cervical spinal cord.

Lubmar enlargemen helps supply LOWER part of the body coming out of lumbar spinal cord.

Conus Medullaris and Terminal, Cauda Equina

Conus medullaris, conical end of the spinal cord ending at L1/L2.
Terminal, tissue running from spinal end down to tall bone.
Cauuda Equina, terminal branching off to other branches.(Looks like a horse tail).

Central Canal. Runs right in middle of spinal cord. Starts right from the fourth ventricle in the brain. Then goes all the way down the spinal cord to the bottom.

Spinal Cord

• White matter surrounds gray matter.

  • White matter has anterior, posterior and lateral funiculus (columns).

• Horns: gray matter has anterior, posterior and lateral horns.

Functions are test send for spinal reflexes.
Its a communication between brain and body.
Sensory tracks going upward coming from the spinal cord being fed to brain.
Motor tracs, impulsed coming down from brain down to spinal cord.

Peripheral Nervous System

Cranial and spinal nerved and branches makes the peripheral.

• made of bundles of fibers.*
  Endoneurium: that covers each and every axon.
  Perineuum: covering the bundle of axon.
  Epineurm: coving the entire nerve.

PNS Cont.

12 nerves makes the cranial nerves.
31 nerve pair of spinal nerves.
Spinal can carry both so makes them mixed. They function mixed. Sensory and motor the can do them both. Called mixed nerves.
some cromial nerves are somatic.
some cranial nerves are autonomic.
Spinal nerver has a dorsal root an ventral root.
Dorsal root is sensory.(In) Root.(Back).
Ventreal rout is motor* (Exit)* Root.(Front).