Chapter 12 Flashcards
Cephalization
Cephalization is the evolutionary development of the rostral (anterior) portion of the CNS
- Cephalization resulted in an increased number of neurons.
- This is the highest level reached in the human brain.
Organization of the brain regions
- Adult brains have 4 regions:
1. Cerebral hemispheres
2. Diencephalon
3. Brain stem, consisting of:- Midbrain
- Pons
- Medulla
4. Cerebellum
Brain regions illustration
Gray matter
Gray matter is short, nonmyelinated neurons and cell bodies.
White matter
White matter is myelinated and nonmyelinated axons.
Cross section of the spinal cord
Ventricles
- Ventricles are any fluid filled chamber that are continuous to one another and to the central canal of the spinal cord.
- Ventricles are filled with cerebrospinal fluid (CSF)
- Ventricles are lined by ependymal cells (neuroglial cells)
- Lateral ventricles (paired): C shaped; deep in each of the hemispheres; separated by a membrane called a septum pellucidum.
- Third ventricle is in the diencephalon;
- Fourth ventricle is in the hind brain which is continuous with the central canal of the spinal cord;
Surface marking on cerebral hemispheres
- Gyri: ridges
- Sulci: shallow grooves
- Fissures: deep grooves
- Longitudinal fissure: separates the 2 hemispheres
- Transverse cerebral fissure: separates cerebrum and cerebellum
Lateral view of the cerebral hemispheres
Several sulci divide each hemisphere into 5 lobes:
- Frontal
- Parietal
- Temporal
- Occipital
- Inusla
The lobes and sulci of the cerebrum
The major sulci that divide the lobes:
- Central sulcus separates pre central gyrus of the frontal lobe and post central gyrus of the parietal lobe.
- Parieto-occipital sulcus separates the occipital and parietal lobes.
- The lateral sulcus outlines the temporal lobes.
Each hemisphere has 3 basic regions:
- The cerebral cortex of gray matter superficially.
- White matter internally
- Basal nuclei deep within the white matter. Basal nuclei is island of gray matter situated deep within the white matter.
The cerebral cortex
- The cerebral cortex is the executive suite of the brain.
- It is a superficial layer of gray matter.
- Mostly made up of neuron cell bodies, dendrites, glial cells and blood vessels.
- Has no axons
- Makes up about 40% of the brain.
4 general considerations of the cerebral cortex:
- Contains 3 types of functional areas:
A. Motor areas: control voluntary movement
B. Sensory areas: conscious awareness of sensation.
C. Association areas: integrate diverse information - Each hemisphere is concerned with contralateral (opposite) side of the body.
- Lateralization (specialization) of cortical function can occur in only one hemisphere.
- Conscious behavior involves the entire cortex in one way or another.
Motor areas of the cerebral cortex
- Located in the frontal lobe, motor areas act to control voluntary movement.
- Primary motor cortex is in the precentral gyrus
- Premotor cortex is anterior to the precentral gyrus
- Broca’s area is anterior to the inferior premotor area.
- Frontal eye field is within and anterior to the premotor cortex; superior to Broca’s area.
The motor areas of the cerebral cortex, illustrated study from this picture
The primary (somatic) motor cortex
- Located in the precentral gyrus of the frontal lobe
- Pyramidal cells - large neuron cell that allow conscious control of precise skilled skeletal muscle movements
- Somatotopy - all of the muscles of the body that can be mapped to an area on the primary motor cortex
Premotor cortex
- Helps plan movements
- Staging area for skilled motor activities
- Controls learned, repetitious, or patterned motor skills
- Coordinates simultaneous or sequential actions
- Controls voluntary actions that depend on sensory feedback
Broca’s Area
- Present in one hemisphere (usually left)
- Motor speech area that directs muscles of speech production
- Active in planning speech and voluntary motor activities
Frontal eye field
Controls voluntary eye movements
Sensory areas of the cerebral cortex
- Areas of the cortex concerned with conscious awareness of sensation
- 8 main areas include:
1. Primary somatosensory cortex allows spatial discrimination and the ability to detect the location of stimulation.
2. Somatosensory association cortex integrates sensory information and produces an understanding of the stimulus being felt.
3. Visual areas
4. Auditory areas
5. Vestibular cortex is responsible for conscious awareness of balance.
6. Olfactory cortex
7. Gustatory cortex
8. Visceral sensory area s are involved in conscious awareness of visceral
sensation.
Multimodal association areas of the cerebral cortex
- Receive inputs from multiple sensory areas.
- Send outputs to multiple areas.
- Allows us to give meaning to information received, store it in memory, tie it to previous experience, and decide on actions.
- Sensations, thoughts and emotions become conscious; this makes us who we are.
- Broadly divided into 3 parts:
1. Anterior association area - prefrontal cortex: intelligent condition, recall and personality; working memory
2. Posterior association area - temporal, parietal and occipital lobes; recognizes patterns and faces; understanding written and spoken language
3. Limbic association area - limbic system; helps establish memories
Lateralization of cortical functioning
- Lateralization: division of labor between hemispheres; The hemispheres are not identical
- Cerebral dominance: refers to the hemisphere that is dominant for language
- 90% of humans have left-sided dominance.
- This usually results in right handedness
- In the other 10%, the roles of the hemispheres are reversed.
Cerebral white matter
- Responsible for communication between cerebral areas, and between the cortex and lower CNS
- Consists of myelinated fibers bundled into large tracts
- Classified according to the direction they run:
- Association (connect regions within the same hemisphere), commissure (connect the hemispheres), and projection fibers (connect each region to other parts of the brain or to the spinal cord).
- Left hemisphere thought to control language thought and logic.
- Right hemisphere is more for visual, spatial skills, intuition, emotion, artistic and musical skills.
- The 2 hemispheres communicate with each other via fiber tracts and functional integration.
White fiber tracts of the cerebral hemispheres
Basal Nuclei (Ganglia)
This is the 3rd of the 3 basic regions of the cerebrum
- Each hemisphere’s basal nuclei include a:
- Caudate nucleus
- Putamen
- Globus pallidus
- Cuadate nucleus + putamen = Striatum
- Function of basal nuclei: Influence muscle movements, play a role in emotion, regulate movement intensity, filter out inappropriate responses.
Basal nuclei illustrated
The diencephalon
- Consists of 3 paired gray matter structures:
1. Thalamus
2. Hypothalamus
3. Epithalamus - All 3 enclose the third ventricle
Midsaggital section of the brain (diencephalon)
** know this!!! **
The thalamus
Function: relay station for info coming into the cortex; sort and relay info coming in; The thalamus mediates sensation, motor activities, memory, cortical arousal, and learning.
Hypothalamus
- Homeostasis: controls autonomic nervous system (BP, heart rate, digestion); initiates physical responses to emotions; Regulates body temp, hunger, water balance/thirst, wake/sleep patterns; Endocrine system.
- The pituitary gland comes off of the hypothalamus.
Epithalamus
- Contains pineal gland
- Secretes melatonin that helps regulate sleep-wake cycle
The brain stem
- Consists of 3 regions: midbrain, pons and medulla oblangata
- Controls automatic behaviors necessary for survival
The midbrain
- Located between the diencephalon and the pons
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Cerebral peduncles
- form the pillars that hold up the cerebrum
- Periaqueductal gray matter - nuclei that plays a role in pain suppression and the fight or flight response.
Pons
- Fourth ventricle separates pons from the cerebellum
- Some nuclei play a role in reticular formation, and some help maintain the normal rhythm of breathing.
Medulla Oblongata
- The medulla contains the choroid plexus: capillary-rich membrane that forms the cerebral spinal fluid
- Medulla is an automatic reflex center
- Many of its functions overlap with the hypothalamus
- The hypothalamus relays instructions via the medulla
- Many of its functions overlap with the hypothalamus
The cerebellum
- 11% of brain mass
- Processes input from the cortex, brain stem, and sensory receptors to provide precise, coordinated movements of skeletal muscles.
- Also plays a major role in balance
Cerebellum anatomy
- Cerebellar hemispheres are connected by wormlike vermis
- Folia: transversely oriented gyri
- Each hemisphere has 3 lobes: anterior, posterior and flocculondular
- Contains a thin cortex of gray matter with a distinctive treelike pattern of white matter called arbor vitae.
- Purkinje fibers originate in the cortex, synapse with the cerebellum
Cerebellum photo
Cerebellum illustrated
Cerebellar Peduncles
- All fibers in the cerebellum are ipsilateral - from and to the same side of the body
- 3 paired fiber tracts connect the cerebellum to the brain stem:
1. Superior Cerebellar peduncles
2. Middle Cerebellar peduncles
3. Inferior Cerebellar peduncles
Cerebellar Processing
The cerebellum fine tunes motor activity as follows:
1. Receives impulses from cerebral cortex of intent to initiate voluntary muscle contraction
2. Receives signals from proprioceptors throughout the body, as well as visual and equilibrium pathways that:
- Pathways continuously “inform” cerebellum of body’s position and momentum
3. Cerebellar cortex calculates the best way to smoothly coordinate muscle contraction.
4. Sends “blueprint” of coordinated movement to cerebral motor cortex and brain stem nuclei.
Cognitive functions of the cerebellum
- Neuroimaging suggests that the cerebellum plays a role in thinking, language and emotion.
Functions of the major brain regions
Functions of the major brain regions 2
Functions of the major brain regions 3
Functions of the major brain regions
Protection of the brain: Meninges
Function of meninges:
- Cover and protect the CNS
- Protect blood vessels and enclose venous sinuses
- Contain cerebrospinal fluid (CNF)
- Form partitions in the skull
The meninges consists of 3 layers (from external to internal)
1. Dura mater - helps to keep the CNS from being jostled around by fastening it to the skull or vertebral column, and supplies a complex system of veinous drainage through which blood can leave the brain.
2. Arachnoid mater - houses the arachnoid space; NO nerves or blood vessels
3. Pia mater - Many blood vessels pass through this layer to supply your brain tissue with blood. It also helps contain cerebrospinal fluid.
look into more details on the 3 layers
Cerebrospinal fluid
CSF forms a liquid cushion of constant volume around the brain.
Functions of the CSF:
- Gives buoyancy to CNS structures
- Reduces the weight of the brain by 97% by floating it so it is not crushed under its own weight.
- Protect the CNS from blows and other trauma.
- Nourishes the brain and carries chemical signals
- CFS is composed of a watery solution formed by blood plasma, but with less protein and different ion concentrations from plasma.
- Choroid plexus - produces CSF in ventricles
The blood brain barrier
- Helps maintain a stable environment for the brain.
- Chemical variations could lead to uncontrollable neuron firings.
- Exceptionally impermeable tight junctions keep the brain separated from many blood borne substances.
- Substances must pass through 3 layers before gaining entry into the neurons
1. Continuous endothelium of capillary walls
2. Thick basal lamina around the capillaries
3. Feet of astrocytes surrounding neurons - The barrier is selective but not absolute
- It allows certain nutrients to move via facilitated diffusion
- Metabolic wastes, proteins, toxins, most drugs, small nonessential amino acids and K+ are denied.
- Allows any fat-soluble substances to pass, including alcohol, nicotine and anesthetics
- Necessary to monitor chemical composition and temperature of blood.
More on the spinal cord
- It is protected by bone, meninges and CSF.
- The spinal dura mater is 1 layer thick (it does not attach to vertebrae)
Epidural space: A cushion of fat and network of veins in the space between the vertebrae and the spinal dura mater. - CSF fills subarachnoid space between arachnoid and pia maters
- Dural and arachnoid membranes extend to the sacrum, beyond the end of the cord at L1 or L2. This is the site of a lumbar puncture or tap.
Conus medullaris
A cone shaped structure where the spinal cord terminates.
Filum terminale
Extends to the coccyx
- Fibrous extension of conus covered with pia mater.
- Anchors spinal cord
Denticulate ligaments
- Extensions of pia mater that secure the spinal cord to the dura mater.
Cervical and lumbar enlargements
Areas where nerves servicing the upper and lower limbs arise from the spinal cord.
Spinal nerves
- Are part of the PNS
- Attach to the spinal cord by 31 paired roots
Cauda equina
A collection of nerve roots at the inferior end of the vertebral column
Spinal cord cross-sectional anatomy
- 2 lengthwise grooves that run the length of the spinal cord partially divide it into right and left halves:
- Ventral (anterior) median fissure
- Dorsal (posterior) median sulcus
- Gray matter is located in the core, white matter outside.
- The central canal runs the length of the cord
- It is filled with CSF
The spinal cord and it’s meningeal coverings
Know this
Gray matter and spinal roots
- 3 areas of gray matter are found on each side of the center and are mirror images:
- Dorsal horns: interneurons that receive somatic and visceral sensory input
- Ventral horns: some interneurons; somatic motor neurons
- Lateral horns: sympathetic neurons
Gray commissure (Gray matter and spinal roots)
A bridge of gray matter that connects masses of gray matter on either side.
- Encloses the central canal.
Ventral roots (Gray matter and spinal roots)
A bundle of motor neuron axons that exit the spinal cord.
Dorsal roots (Gray matter and spinal roots)
Sensory input to the spinal cord
Dorsal root (spinal) ganglia (Gray matter and spinal roots)
Cell bodies of the sensory neurons
Spinal nerves (Gray matter and spinal roots)
Formed by the fusion of the dorsal and ventral roots.
Gray matter is divided into 4 groups based on somatic or visceral innervation
- Somatic sensory (ss)
- Visceral sensory(VS)
- Visceral (autonomic) motor (Vm
- Somatic motor (SM)
Visceral = automatic
Somatic = in our control
White matter (spinal cord cross sectional anatomy)
- Myelinated and nonmyelinated nerve fibers allow communication between parts of the spinal cord and brain.
- Run in 3 directions:
- Ascending: up to higher centers (sensory inputs)
- Descending: from brain to cord or lower cord levels (motor outputs)
- Transverse: from one side to the other (commissural fibers)
White matter is divided into 3 white columns (funiculi) on each side:
- Dorsal (posterior)
- Lateral
- Ventral (anterior)
Each spinal tract is composed of axons with similar destinations and functions
Ascending tracts and descending tracts of the spinal cord
White matter vs Gray matter in the spinal cord
Gray matter receives input within the spinal cord and relays information out.
White matter is involved with communication between the brain and spinal cord (up and down).
