Central Nervous System Dr. Anderson GCIT

Animal Body Plans

Cephalization Organisms that have a proper and distinct “head end” Why is this important?

Cephalization

Major Divisions Brain Spinal Cord Processes information coming in from afferent nerves Sends signals (motor) out to body via spinal cord and cranial nerves Spinal Cord Connects brain to peripheral nerves May also initiate motor responses (reflexes)

Brain Divisions - Anatomical Cerebrum (Cerebral Hemispheres) Diencephalon Brain Stem (Pons, midbrain, medulla) Cerebellum Each of these divisions can be divided further, into anatomical AND functional divisions

Brain Ventricles “Spaces” in the brain that are left over from embryonic brain development Spaces are filled with cerebro-spinal fluid Why?

Hydrocephaly “Water on the brain” Pressure inside the brain inceases due to too much cerebro-spinal fluid (CSF) being produced or drainage is blocked

Functional Anatomy

Major Brain Divisions

Cerebrum

Cerebrum Divided into hemispheres bilaterally Each half of the cerebrum is further divided into regions by: Gyri “Twisters” Sulci “shallow grooves” Fissures “Deeper grooves”

Major Fissures Longitudinal Fissure Transverse cerebral fissure

Major Sulci and Gyri

Brain and Skull Frontal lobes lie within the anterior cranial fossa The anterior parts of the temporal lobes lie within the middle cranial fossa The posterior cranial fossa houses the brain stem and cerebellum

Cerebral Cortex Only 2-4 mm thick, but 40% of brain mass Contains BILLIONS of neurons (convolutions increase surface area) Functional areas can be identified, but all areas of the cortex are interconnected Each hemisphere is associated with the opposite side of the body (laterally)

Stroke People that have motor areas affected on only one side of their brain Opposite part of the body may be paralyzed

Cortex – Thin Shell of Grey Matter

Functional Cortex Areas Motor – initiates movement in areas of the body Sensory – Sensations from the body come here to be processed Association Areas – where incoming information from the body is processed

Motor and Sensory Areas

Primary Motor Cortex Located in the pre-central gyrus Pyramidal cells – allow conscious control and coordination of voluntary movements Connect to spinal cord (pyramidal tracts) Motor areas are not simply discrete, but interconnected!

Premotor Cortex Anterior to precentral gyrus Provides a ‘memory bank’ for skilled motor activities Also controls motor activity that rely on sensory feedback

Outline the Primary and Premotor Cortices

Broca’s Areas Control the muscles that are responsible for speech Also active during “planning” of motor activities Would you expect this area to be smaller or larger in chimps (our closest animal relative)?

Outline Broca’s Areas

Frontal Eye Field Lies anterior (and within) premotor cortex Controls voluntary movements of the eyes

Sensory Areas – Primary Somatosensory cortex Post-central gyrus of the parietal lobe Neural input from the skin and proprioreceptors (from muscles and joints) is decoded and the stimulated body part is identified (spatial discrimination)

Somatosensory Association Cortex Integrates sensory inputs to produce an understanding of what is being felt DEMO What would damage to this area do?

Label the Primary and Association Somatosensory Cortices

Primary Visual Cortex Receives input from the cells in the retina of the eye

Visual Association Cortex Uses past visual stimuli “visual memories” to determine what is being seen Uses different aspects of the visual data (shape, contrast, depth perception, etc.)

Primary Auditory Cortex Superior margin of temporal lobe Gathers data on pitch, loudness and location (by the difference in impulses received by each ear) Auditory Association Area – interprets sound by relating to past auditory memories

Olfactory Cortex On medial aspect of temporal lobe Part of the old “rhinencephalon” (nose brain) that still exists Most of the rest of our ancestral rhinencephalon has evolved to process “higher” emotions – the limbic system

Auditory and Olfactory Cortices

Insula Part of the cerebral cortex that is just deep to the temporal and frontal lobes Seen when temporal lobe is retracted

Other Cortices Gustatory Cortex - Perceives taste stimuli Just deep to temporal lobe (on the insula) Visceral Cortex – Perceives information from the gut Just posterior to gustatory cortex Vestibular Cortex – provides information about the position of the head in space Posterior of insula

Multimodal Association Areas Generally receives information after being processed by the association cortices for each sense Receives input from multiple stimuli, and Give meaning to it Devote it to memory Act upon it Relate it to previous experience Senses related to conciousness

Motor Homonculus (cortical)

Somatosensory Homonculus

Anterior Association Area In frontal lobe Center for Intellect Personality Judgement Planning Abstract Ideas

Posterior Association Area Temporal, parietal, occipital lobes Allows to recognize: Patterns and faces Localizing yourself in space Self-awareness

Limbic Association Area Includes the singulate gyrus, hippocampus Provides emotional impact that is tied to certain situations Example?

Lateralization Each hemisphere of the brain is functionally identical However, each hemisphere is considered to be functionally different (slightly) in higher brain functions, but research continues “Left-brain” – math, logic, language “Right-brain”- art, music, creativity

Cerebral White Matter Deep to the cortex Connects “grey matter” cortices to each other and to the lower CNS (spinal cord) White color is due to the myelination of the fibers composing the tissue

Grey and White Matter Distribution

White Matter Fibers Commissures – Connect corresponding grey matter of the two brain hemispheres Allows them to act together Association Fibers – Connect different parts of the same hemisphere Projection Fibers – connect the brain to the rest of the nervous system (spinal cord)

Diencephalon Forms the core of the forebrain (surrounded by cerebral hemispheres) 3 major divisions Thalamus Hypothalamus Epithalamus

Thalamus Consists of 2 bilateral egg-shaped “nuclei” Serves as a relay station for all impulses entering the brain All afferent impulses are directed to the relevant areas of the brain All efferent impulses are directed to the relevant areas of the body

Hypothalamus Located inferior to the thalamus The main visceral control center of the body, maintains homeostasis

Hypothalamus Functions Autonomic control center Heart rate, blood pressure, digestive tract movements, etc. Emotional Responses Pleasure, fear, rage, sex drive Body Temperature Fever, sweating, shivering,

Hypothalamus Functions (con’d) Food intake Monitors glucose levels in the blood Water balance and thirst Monitors levels of solute concentrations in the blood Sleep-wake cycles Major controller of the endocrine system

Epithalamus Most dorsal portion of the diencephalon Most notably contains the pineal gland, which secretes the hormone melatonin Helps regulate the sleep-wake cycle

Brain Stem Directly inferior to diencephalon Three major areas Midbrain Pons Medulla Oblongata

Midbrain Function Fight-or-flight response Visual reflex centers (visual tracking) Startle reflex

Pons Helps to maintain the normal rhythm of breathing Serves as a bridge between the motor cortex and the cerebellum

Medulla Oblongata Located just in the opening of the foramen magnum (top of spinal cord) Regulates many homeostatic functions Cardiovascular regulation Respiratory rhythm Hiccuping, coughing, vomiting, swallowing, sneezing

Cerebellum Bilaterally symmetrical organ that occurs inferiorly to the occipital lobe Times our efferent motor impulses, resulting in smooth coordinated movements

Cerebellar Processing Cerebral motor areas relay their intent to start voluntary muscle contraction Afferent impulses from proprioreceptors send information about body position and momentum Cerebellar cortex calculates the amount and direction of muscle contraction needed to complete the action The “plan” of motion is sent back to the motor areas of the cerebrum, where impulses are sent for the action to be executed

The Limbic System Our “emotional” brain Composed of organs that surround the upper brain stem Rhinencephalon Cingulate gyrus Amygdala Hypothalamus Fornix

Emotional Brain Amygdala Cingulate gyrus Recognizes fearful facial expressions Core of the fear response Cingulate gyrus Helps to express emotions as gestures Resolves mental conflicts

Crossed Communication Even Numbers The limbic system communicates directly with the frontal lobe via white matter. Odd Numbers Most limbic system actions are regulates by the hypothalamus What issues might these connections cause??

The Reticular Activating System The reticular neural formation extends from the brain stem into many major areas of the brain Makes this system ideal for arousing the brain as a whole The RAS filters out “typical” stimuli, but arouses the brain when something unusual or significant happens

Levels of Consciousness Alert Drowsy/Lethargic Stupor Coma What causes us to shift along this continuum?

Memory The storage and retrieval of information Memories are stored in parts of the brain that need them (e.g. visual association cortex for memories of shapes) What affects the vividness and length of memories? Emotional State Repetition Association (mnemonic devices)

Protection of the Brain Meninges (Physical protection) Cerebrospinal Fluid (Physical Protection) Blood-Brain Barrier (Chemical Protection and Immune Function)

Meninges Sheets of fibrous connective tissue that surrounds the brain Dura Mater Continues inferiorly as the spinal dura mater Arachnoid membrane Pia mater

Dura Mater

Cerebrospinal Fluid Fills the spaces in and around the brain and spinal cord Ventricles Meninges Absorbs shock, provides buoyancy and delivers materials (electrolytes, etc.) to the brain

Spinal Tap CSF may need to be sampled to check for infection/injury No blood/bacteria should be isolated from CSF in healthy individuals

Blood-Brain Barrier Brain needs to be protected from Pathogens Wild swings in chemistry Capillaries serving the brain are only permeable to the smallest molecules essential for brain function Tight junctions in blood vessel epithelia Astrocytes – limit what comes in and out of brain tissue Always a good thing?

Concussion Generally due to a violent jarring or twisting of the brain inside the cranium

Progressive Brain Diseases What types of diseases are responsible for slow, progressive loss of mental function? Name of disease Symptoms Mode of pathology Prognosis Treatment

Spinal Cord - Anatomy Enclosed by the neural arches of the vertebrae Extends from the base of the skull to the 1st-2nd lumbar vertebrae

Spinal Cord - Function Provides afferent and efferent nerve pathways to and from the brain and peripheral nerves Major reflex center

Spinal Cord – Protection Resides within the spinal canal (vertebrae) Also surrounded by meninges Spinal Dura Mater Arachnoid Membrane Pia Mater CSF between arachnoid membrane and pia mater

Spinal Meninges

Epidurals Anesthetic is placed in epidural space using a fine needle (catheter) Often used during labor, surgery or diagnostic procedures

Spinal Cord Terminus Spinal cord ends at the conus medullaris at 1st-2nd Lumbar vertebra Filum terminale anchors the spinal cord to the coccyx Nerve roots for lumbar and sacral region extend through the vertebral canal and exit through their respective vertebrae

Cauda Equina

Spinal Cord Cross-Sectional Anatomy