Brain Anatomy and Function

Nervous System Overview

• The nervous system serves as the body's master controller, regulating all bodily functions.
• Cells communicate through electrical and chemical signals
• The system is excitable and conductive, meaning it can be stimulated and transmit signals.
• The three key overlapping functions of the nervous system are sensory input, integration, and motor output.
  • Sensory input involves monitoring stimuli.
  • Integration processes and interprets sensory input.
  • Motor output responds to stimuli by activating effector organs to produce a response.

Organization of the Nervous System

• The nervous system is divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
  • The CNS comprises the brain and spinal cord and acts as the integration and command center.
  • The PNS includes spinal and cranial nerves that carry messages to and from the spinal cord and brain.
• Functional divisions of the PNS include:
  • Sensory (afferent) division, which carries impulses from the skin, skeletal muscles, and joints to the CNS via sensory afferent fibers. It also transmits impulses from visceral organs to the CNS via visceral afferent fibers.
  • Motor (efferent) division, which transmits impulses from the CNS to effector organs.
• Further divisions of the motor division include:
  • Somatic Nervous System, which allows conscious control of skeletal muscles.
  • Autonomic Nervous System (ANS), which controls visceral motor nerve fibers, regulating smooth muscle and glands.
• Branches of the Autonomic Nervous System:
  • The sympathetic nervous system controls the "fight or flight" response
  • The parasympathetic nervous system controls "rest and digest" functions.

Central Nervous System - Brain and Spinal Cord

• The four main adult brain regions are:
  • Cerebral hemispheres (left and right sides).
  • Diencephalon (middle region).
  • Brain Stem (midbrain, pons, medulla).
  • Cerebellum (in back).

Cerebral Cortex

• The cerebral cortex is the outer layer of the brain made of gray matter (unmyelinated neurons).
• The cortex is arranged into folds, increasing the surface area and number of neurons.
• Underneath the cortex lies white matter (myelinated neurons).
• There is are association nerves and tracts for memories.
• The cerebral cortex is divided into two contralateral hemispheres.
• The cerebral cortex is the executive suite of the brain.
• Conscious mind awareness, sensory perception, and motor control occur in the cerebral cortex
• The superficial layer of gray matter is 2-4 mm thick.
• It is composed of neuron cell bodies, dendrites, glial cells, and blood vessels, but no axons.
• Dendrites make up 40% of the neuron mass.

General Considerations of the Cerebral Cortex

• Major considerations are that the cerebral cortex:
  • Contains motor areas (control voluntary movement), sensory areas (conscious awareness of sensation), and association areas (integrate diverse information).
  • Each hemisphere is concerned with the contralateral side of the body.
  • Lateralization of cortical function can occur in only one hemisphere (left vs. right-handed).
  • Conscious behavior involves the entire cortex in one way or another.

Corpus Callosum

• The corpus callosum connects the hemispheres, allowing them to communicate.
• It consists of white myelinated association fibers which has a covering, resulting in fast signals.

Brain Lobes and Their Functions

• The five lobes of the brain are:
  • Frontal lobe is responsible for:
    • Personality and intellect.
    • Broca's area controls the muscles of speech
    • Somatic Motor Cortex controls motor to skeletal muscles, voluntary, located in the precentral gyrus.
    • Premotor association Area develops learned movements.
    • Frontal Eye field controls eye movement.
    • ½ of Olfactory Cortex controls the sense of smell-Split.
  • Parietal Lobe:
    • Somatosensory Cortex: sensory inputs from body tissues, located in postcentral gyrus
    • Somatosensory Association Area: memories + understandings areas
    • Wernicke's Area (shared w/temporal lobe): ability to understand speech- words
  • Temporal Lobe:
    • Auditory Cortex: hearing and interpretation capabilities
    • Auditory Association Area: contains sounds, cat v.s. dog sound
  • Occipital Lobe:
    • It contains: -Visual cortex: visual input -Visual association area: understanding + memory of visuals
• The limbic system is responsible for:
  • Memory and emotions.
    • Insula (deep to temporal lobe):
      • Vestibular Cortex: balances body
      • Visceral Association Area: monitors all visceral input-stomach ache, full bladder
      • Gustatory Cortex: allows for memories and tastes

Homeostatic Imbalance

• Damage to areas of the primary motor cortex causes paralysis of the muscles controlled by those areas.
• Paralysis occurs on the opposite side of the body from the damage.

Diencephalon

• The diencephalon is the area below the cortex, formed by the thalamus, hypothalamus, and epithalamus.
  • The Thalamus "post office to brain", sorts and sends signals to the right area
  • The Hypothalamus controls the ANS, regulates hunger, thirst, and temperature, controls most endocrine functions, and is associated with the limbic system and emotions.
  • The Epithalamus contains the pineal gland (body), and secretes melatonin to regulates sleep cycle

Brain Stem

• The brain stem attaches the brain to the spinal cord and is made up of the midbrain, pons, and medulla oblongata.
  • The Midbrain contains the corpora quadrigemina, which mediates reflexes for hearing and vision.
  • The Pons contains tracts and regulates respiration.
  • The Medulla Oblongata connects to the spinal cord and regulates vitals such as heart rate, blood pressure, and respiration rate. Also regulates other "automatic" functions like Emesis, Urinary, and Defecation The Reticular Formation consists of gray matter in the brainstem that regulates visceral activity and consciousness.

Cerebellum

• The cerebellum coordinates skeletal muscle activity and monitors joint position.
• It contains gray and white matter, with white matter called the Arbor Vitae.
• Damage to this area can cause ataxia, resulting in drunken and uncoordinated movements.

Meninges

• Meninges are coverings around the CNS made up of three layers:
  • Dura mater (thickest layer that attaches to the skull).
  • Arachnoid mater (middle layer forms the subarachnoid space and drains CSF into veins).
  • Pia mater (thin and delicate layer directly over the brain).

Meningitis

• Meningitis is the inflammation of the meninges which can spread to the CNS.
• Diagnosed by observing microbes in a sample of CSF from a lumbar puncture.

Cerebral Spinal Fluid

• CSF supports and nourishes the brain, allowing it to float in fluid.
• CSF is formed by the choroid plexus and is drained by arachnoid villi.

Homeostatic Imbalance: Hydrocephalus

• Hydrocephalus occurs when an obstruction blocks CSF circulation or draining.
• This results in increased pressure.
• In newborns, the skull bones are unfused, so increased pressure causes the head to enlarge.
• In adults, increased pressure can lead to brain damage as the brain can't expand.

Ventricles of the Brain

• Ventricles of the brain:
  • are the brain's chambers filled with CSF.
  • are lined with ependymal cells used to move the CSF with Cilia.
  • are connected to one another + the spinal cord -The lateral ventricles connect to the 3rd ventricle. -The 3rd and 4th ventricles link via the cerebral aqueduct.

Protection of the Brain

• The four structures that provide protection to the brain are meninges, cerebrospinal fluid, cranium, and the blood-brain barrier.
• The Blood-Brain Barrier:
  • Selective barrier between blood vessels of the brain and nerve cells which allows glucose, amino acids, and electrolytes to pass through, but blocks metabolic waste, proteins, some toxins, and most drugs
  • Is lacking around parts of the brainstem and the hypothalamus.

Problems in the Brain

• Problems in the brain include:
  • CVA (stroke) - blood vessel bursts, leading to temporary episodes of reversible cerebral ischemia.
  • Ischemia - a blood vessel is blocked, resulting in loss of O2 and blood flow, leading to the loss of brain tissue.
  • Concussion - brain injury causing a bruising of the organ, can result in damage.
  • Coma - prolonged state of unconsciousness, reticular formation affected, usually caused by injury or medicine (drug overdose).
  • Alzheimer's disease (AD) - progressive, degenerative disease of the brain that results in dementia.

Spinal Cord

The spinal cord:

• Is constructed with gray + white matter
• Has white matter concentrated in the outer areas of the cord for faster signaling
• IS protected by bone, meninges, Cerebral Spinal Fluid- the Dura Mater IS NOT attached to the vertebrae
• Conus medullaris: Is where the spinal cord ends
• Is cushioned by fat
• Dural + arachnoid membranes cover the spinal cord, allowing for a site of Lumbar Puncture

Spinal Nerves

• 31 pairs of spinal nerves exit off of the spinal cord through the intervertebral foramen.
  • Spinal nerves classified as: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.
• Nerve fibers extend from the ventral and dorsal aspect of the spinal cord.
• Dorsal Roots are located in the back( they are mostly sensory)
• Ventral roots are located in the brain( they are mostly motor, and most commonly pinched with bulging disks)

Spinal Cord Tracts

• The main spinal cord tracts are:
  • Prymidal tract (motor,ventral,)
  • Fasciculus (sensory, dorsal), including the Cuneatus (arms), and Gracilis (legs).

Peripheral Nervous System

• Made of the nerves that extend off of CNS, from nerve fibers or axons
• Can be sensory motor, or BOTH.
• PNS differs from cranial nerves where the PNS main divisions are spinal nerves , head and neck signals need cranial nerves
• Quicker = reflexes

Reflexes

• Predictable, quick responses
• Involve in pathway or constant sensory nerve > CNS > motor nerve
• Label parts such as Sensory neuon , motor nueron, and effector muscle
• Refexes are quicker

Automatic Nervous System

• This is involuntary with body activities
• controls - Blood flow, heart rate, digestion, respiration rate, hormones
• centered in the hypothalamus
• Parasympathetic is for rest and digest
• Sympathetic is fight and flight with -prepare is body for action
• Uses what to enhance epinephrine / adrenaline Changes in the body:
  • increase heart rate or respiratory rate
  • Pupils dilate or blood flow
  • decrease digestion activity

PNS

• Decrease activity in Cranial Sacral
• Increase in : Digestion metabolism
• Main transmitter: ACH

Histology of Tissue Nerve

• Highly cellular with a little extracellular space
• Tightly filled
• 2 main: nerves - carry action potential, impulse signals, very tight, connect, defend

Astrocytes

• Supportive
• Highly brancked
• connects, braces, nutrients, barriers blood

Microglia

• Phagocyte
• Small round with prcecesses
• Detects, then phagocytosis to remove waste.
• Does not form inflammation

Ependyval

• squamous, cilicated
• Cilia helps with circulation

Oligodendrycites

• large, create myelin sheath

Schwann

• Small - surrounds PNS fibers
• Makes sheath
• can regenerate

Satellite

• similar to the job of an astrocyte but cushioned

Nueons

• Make action potential
• High cell with + projected out
• Long life, metabolic
• Can electrical + signal things

Nueon

• cell body + extensions - 2 of them - bundles of processes = tracks in NS
• Can have one-way transmissions

Neuron

• Dendrites that are short
• Axons that are long
• Major parts are cell body, Axin, + dendrites

Denrites

• Highly branched
• carry message to cell body

Axon

• Attached to the cell with the axon transmitting

Minor parts, such as - Axons, Hillrock, ect.

Major type of neuroglia

Cell - body

• Astrocytes, connect, protects, and defends

Explore brain structures like the hypothalamus, cerebellum, and brainstem, and their roles. Understand the function of the thalamus. Learn about the protective layers of the brain and how myelin sheaths affect nerve signal transmission.