Chapter 15: Brain and Cranial Nerves
Terms in this set (51)
Overview of Brain
Capable of controlling a multitude of activities simultaneously and respond to a variety of stimuli with an amazing degree of versatility
Does size determine intelligence?
The # of active synapses among neurons determines intelligence; it's all about the wiring
Major structures of superficial Brain
- lobes (frontal, temporal, occipital, and parietal)
- Sulci (central, lateral, parieto-occipital)
- Brainstem (Pons and Medulla)
- Spinal Cord
What is the point of gyri and sulci?
to increase surface area
What is Lessencephaly?
when you have 0 sulci; most are severely mentally retarded and experience seizures
Embryonic Development of the Brain
- begins at rostral end of cylindrical, hollow neural tube
- grows at disproportionate growth rates in different regions
- restricted by membranous skull
- the convulsions formed are sulci and gyri
What are the 2 main flexures of the membranous skull and what do they do?
midbrain and cervical; they bend the brain towards the brain stem to fit the brain into a small space
What are the distinct tissue areas and what do they contain?
- Gray Matter contains motor/interneuron cell bodies, dendrites, telodendria, and UNmyelinated axons; on outside
- White Matter contains myelinated axons; on inside
What protects and isolates the brain?
- Cranium: rigid support
- Meninges: protect, support, and partition brain
- Cerebrospinal Fluid: cushioning fluid
- Blood-Brain Barrier: prevents entry of harmful substances from the blood stream into the brain
- Tight Junctions: seals the capillary to make it hard for things to go through
What are the cranial meninges?
Pia Mater (deepest), Arachnoid Mater, and Dura Mater (outermost)
What are the functions of the meninges?
- separate soft tissue of the brain from the skull
- enclose and protect blood vessels
- forms partitions within the skull
- helps brain float in the skull
- circulates CSF
- assist in draining blood from the brain (but only in select regions like the dural venous sinuses)
What are the brain ventricles?
cavities or expansions within the brain that are derived from the lumen of embryonic neural tube; they are continuous with one another and connect with the central canal of the spinal cord; filled with fluid and lined by ciliated ependymal glial cells
What are the different brain ventricles?
- Lateral Ventricles: in the cerebrum separated by septum pellueidum
- 3rd Ventricle: connects with lateral ventricle through interventricular foramen and cerebral aquaduct passes through midbrain to connect to the 4th Ventricle
- 4th Ventricle: narrows at end and connects with central canal in the spinal cord
What is cerebrospinal fluid (CSF)?
clear, colorless liquid found in and around the brain and spinal cord; circulates in the partitions of the brain; originates from blood plasma in the choroid plexus and is similar to blood plasma but differs in proteins and mostly IONS
What are the functions of CSF?
- Buoyancy: lets brain float and supports more than 95% of its weight and prevents it from bring crushed under its own weight
- Protection: liquid cushion to protect delicate neural structures from sudden and forceful movements
- Environmental Stability: transports nutrients and chemicals to the brain and removes waste products form the brain and protects nervous tissue from chemical fluctuations
What is the Choroid Plexus?
- located hanging from the roofs of ventricles
- forms and cleanses CSF
- represents a cluster of thin-walled capillaries enclosed by a layer of ependymal cells supported by the pia mater
How does CSF circulate?
- 150 mls total CSF in adults, produce 500ml per day so entire volume is replaced every 8hrs
- Is continually removed from subarachnoid space via arachnoid villi to the venous circulation so that it won't accumulate and compress and cause damage/trauma/swelling to the nervous tissue
- congestion can causes sinuses to let venous blood circulate
- Works on a self-Regulated System - when pressure drops, the flaps close; the arachnoid villi are the pressure sensors
Steps of CSF circulation?
1. produced by choroid plexus by ventricles
2. flows from lateral ventricles through interventricular foramen to the 3rd ventricle and through the cerebral aqueduct into the 4th ventricle
3. Flows into subarachnoid space by going through either the paired lateral apertures or the median aperture into the central canal of the spinal cord
4. removes waste products and provides buoyancy as it flows through the subarachnoid space
5. excess CSF flows into the arachnoid villi and then drains into the dural venous sinuses - the greater pressure in the subarachnoid space ensures that CSF moves into the venous sinuses without letting blood enter the subarachnoid space
What kind of thought does the cerebrum control?
intelligence, reasoning, perception, thought, memory, and judgement along with voluntary motor/visual/auditory activities
- comprised of 2 large hemispheres on superior aspect of the brain that fit snugly into the skull
- difficult to assign precise function to each specific side
- both hemispheres receive sensory information from and project motor commands to the opposite side of the body
What are the functional areas of the cerebrum?
- Motor areas: control voluntary motor functions (frontal lobe)
- Sensory areas: conscious awareness of sensation (parietal lobe, occipital lobe, temporal lobe, and insula)
- Association areas: integrate and store information (auditory association area, visual association area, and somatosensory area)
- Places of integration from many association areas from different lobes: Wernicke Area, Gnostic Area, and Broca Area
What is the Wernicke Area?
Place of recognizing, understanding, and comprehending spoken or written language
What is the Gnostic Area?
place of integrating all sensory, visual, and auditory info being processed within these lobes
What is the Broca Area?
place of language comprehension and various speech and language function
What is the motor and sensory homunculus?
- topography of primary motor cortex and primary somatosensory cortex in the coronal section
- shows the innervation of motor/somatosensory cortex to various body parts; size of the structure on homunculus indicates the degree of control (smaller=more precise)
What is central white matter?
composed primarily of unmyelinated axons grouped into bundles (tracts)
How is central white matter classified?
- association tracts: communication within a hemisphere; arcuate fibers and longitudinal fasciculi
- commissural tracts: communication between corresponding hemisphere regions; function as a coordinated whole
- projection tracts: connect cortex to caudal brain and spinal cord and is the predominant portion of white matter
What is the difference between arcuate and longitudinal fibers?
Arcuate Fibers: connect neighboring gyri within a single lobe Longitudinal Fibers: connect gyri between different cerebral lobes of the same hemisphere
What are cerebral nuclei?
- paired, irregular masses of gray matter that are found deep within white matter
What are the components of cerebral nuclei?
- Caudate nucleus: control pattern/rhythm of arm and leg movement associated with walking
- Lentiform nucleus: control muscle movement at subconscious level - Putamen; Excites/inhibits thalamus to control/adjust muscle tone - Globus Pallidus; overall it fine tunes, coordinates, and adjusts signal for movement
- Claustrum: process visual info at subconscious level
- Amygdaloid body: controls expression of emotion, behavior activities, and development of mood -- Limbic System
What is the Diencephalon and what does it do?
- comprised of the epithalamus, thalamus, and the hypothalamus
- provides the relay and switching centers for some sensory and motor pathways and for control of visceral activities
What does the pineal gland do?
- contains pineal gland (secretes Melatonin to regulate body's circadian rhythm) and habenular nuclei (relay for limbic system and visceral and emotional repsonse to odors)
What does the Thalamus do?
- comprised of thalamic nuclei (all gray matter organized in groups by function and the axons project to a particular region of cerebral cortex)
- serves as a principle and final relay point for sensory information to be processed and projected to sensory cortex except olfaction
- "Information filter": only small amount of info is forwarded to the cerebrum
- "clues in" the cerebrum to where the the info came from
What does the Hypothalamus do?
- a thin, stalklike infundibulum extends inferiorly to attach to the pituitary gland
- it deals with homeostatic control
What are the functions of the hypothalamus?
- master control of the autonomic nervous system and endocrine system
- regulation of emotional behavior and of sleep-wake (Circadian) rhythms
- control of food and water intake
What is the brainstem?
- connects cerebrum, diencephalon, and cerebellum to spinal cord
- represents a bidirectional passageway for all tracts between cerebrum and spinal cord
- contains autonomic centers and reflex centers required for survival and houses nuclei of many cranial nerves
What does the midbrain contain?
- Cerebral peduncles: pyramidal motor tracts on the surface descend to the spinal cord and act as primary skeletal muscle activators
- Cerebral aqueduct: connects 3rd and 4th ventricles
- Tectum (tectal plate): relay stations in the processing pathway of visual and auditory sensations
- Pigmented Nuclei: Substantia Nigra (relays inhibitory signals to cerebral nuclei to regulate motor output to skeletal muscle and Red Nucleus (functions are "debatable")
- Reticular Formation: loosely organized gray matter core in the brain
What are the 2 parts of the tectal plate and what do they do?
- Superior Colliculi: eye and head movement and visual reflexes
- Inferior Colliculi: startle reflex and auditory reflexes
What is Parkinson's disease?
result of degeneration of substantia nuclei
What does the Pons do?
- mainly composed of conduction tracts
- autonomic respiratory center
- influences and modifies medullary respiratory center activity
- holds sensory and motor tracts that connect to brain and spinal cord
What is the Medulla?
where the pons blends into spinal cord at foramen magnum
What does the medulla contain?
- 2 longitudinal ridges: pyramidal tracts and pyramids
- olive (olivary nuclei): large fold of gray matter that functions to relay sensory proprioception info to cerebral cortex
- vomiting, gagging, swallowing, salivation, coughing, and sneezing control
- autonomic nuclei
What is decussation of pyramids?
axons cross to opposite sides in the medulla and control opposite hemispheres
What are the autonomic nuclei and what do they do?
- cardiovascular centers: regulates both the heart's rate and strength of contraction
- respiratory centers: regulates the respiratory rate and influenced by the Pontine Respiratory Center in the pons
What is the cerebellum?
- second largest part of brain
- bilaterally symmetrical
- contains a thin outer cortex of gray matter, internal white matter (arbor vitae), and deep, paired masses of gray matter (folia)
What structures does the cerebellum contain and what do they do?
- The anterior and posterior lobes of each hemisphere coordinate body movements
- The Flocculonodular lobe adjusts posture to maintain balance
What kind of fibers are entering and exiting the cerebellum?
What are the functions of the cerebellum?
- overall function is to coordinate and "fine-tune" skeletal muscle movements
- ensures correct pattern for smooth coordinated movements
- stores memories of previously learned movements
How does the cerebellum function?
functions subconsciously: performed indirectly (without having to be actively initiated
What is the Limbic System?
- "collective name" for brain structures
- composed of cerebral and diencephalic structures
What does the limbic system do?
- involved in motivation, emotion and memory with an emotional association
- affects memory formation-integrates past memories of physical sensations with emotional states
- involved in the development and expression of emotional reactions ("emotional brain")
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