Ch. 11 The Nervous System Part 1: The Brain …tokaybiology.weebly.com › uploads › 5 › 5 › 6...

©2019 McGraw-Hill Education.

Ch. 11 The Nervous SystemPart 1: The Brain

(Interactive pages 390-409)


Characteristics of the Central Nervous System

• The Brain• 1011 multipolar neurons…that’s 100,000,000,000

• Outer layer of Gray Matter (cell bodies & unmyelinated axons)

• White Matter underneath (myelinated axons)

• The Spinal Cord• Central gray matter

• White peripheral matter (axon extending up and down from

brain)

• Connects to brain via brain stem

• Axons directing impulses up to brain = ascending

• Axons directing impulses down from brain = descending


11.2 MeningesMembranes between the bone and soft tissues that protect brain and spinal cord

3 layers (outer to inner):

Dura mater: (internal periosteum of the skull)

• Tough, dense connective tissue

• Blood vessels and nerves

• Continues down into vertebral canal

• Epidural space lies between Dural sheath and bone

Arachnoid mater:

• Thin and web-like, avascular

• Subarachnoid space contains cerebrospinal fluid (CSF).Pia mater:

• Inner layer; attached to surface of brain, spinal cord.

• Blood vessels & nerves.

• Nourishes CNS.


Figure 11.1 Meninges

©McGraw-Hill Education


Figure 11.2 Meninges of the Spinal Cord


11.3 Ventricles and Cerebrospinal Fluid (CSF)

• Ventricles

• Interconnected cavities of the cerebral hemispheres and brain stem filled with cerebrospinal fluid (CSF)

• Continuous w/ central canal of spinal cord

• 2 Lateral Ventricles (in L & R Hemispheres

• Third Ventricle (under corpus callosum)

• Fourth Ventricle (anterior to cerebellum)

• Cerebrospinal Fluid (circulates in ventricles, central canal, & sub arachnoid space)

• Secreted by the Choroid Plexuses in Pia Mater

• Capillaries covered by ependymal cells connected by tight junctions

• Like blood/brain barrier with prevents water soluble substances from blood getting into CSF

• Clear Viscous liquid

• Protective and Nutritive

• High in sodium/low in glucose and potassium

• After exchanging substances, CSF is absorbed by the arachnoid granulations.


Figure 11.3 Ventricles of the Brain


Figure 11.4 Cerebrospinal

Fluid

• Circulates in ventricles, central canal of spinal cord, and subarachnoid space.

• Volume is about 140 ml at any time.


Clinical Application 11.2

Cerebrospinal Fluid Pressure

• Continuous secretion and reabsorption of cerebrospinal fluid (CSF) keeps fluid pressure in ventricles constant.

• Interference with circulation of CSF (by infection, tumor, blood clot) can increase intracranial pressure (ICP) in ventricles.

• Can lead to collapse of cerebral blood vessels, injury of brain tissues compressed against skull.

• Spinal tap / lumbar puncture is used to measure CSF pressure.

• Pressure can be relieved by insertion of a drain into subarachnoid space.

• Hydrocephalus in infant (“water on the brain”) can be treated by insertion of a shunt.



Traumatic Brain Injury

Traumatic Brain Injury (TBI): result of mechanical force such as a fall, attack, accident, sports injury

Concussion: a mild TBI; typically results from a one-time injury and has no lasting symptoms

Chronic traumatic encephalopathy (CTE): sports-related, mild repetitive TBI; results from many small injuries over time; symptoms begin years later and have long-lasting effects on memory and behavior

Blast-related brain injury: Severe TBI, resulting from explosions in combat situations; often leads to cognitive decline years after injury

https://www.youtube.com/watch?v=VB1Bos0LUnE&t=2s

https://www.youtube.com/watch?v=VB1Bos0LUnE&t=2s


The Brain

Functions:

• Neural centers for sensory function.

• Sensations and perceptions.

• Motor commands to skeletal muscles.

• Higher mental functions, such as memory, reasoning.

• Neural centers for coordinating muscular movement.

• Neural centers for regulating visceral activities.

• Personality.

©2019 McGraw-Hill Education. bottom: © Martin M. Rotker/Science Source

4 Major portions of the brain:

• Cerebrum.

• Diencephalon.

• Cerebellum.

• Brainstem.


Brain Development• Begins as neural tube in embryonic

development

• Forebrain (prosencephalon)

• Anterior Telencephalon

• Lateral Ventricles, Cerebrum, & Basal Nuclei

• Posterior Diecephalon

• 3rd Ventricle, Thalamus, HypoTh., Pituitary, & Pineal Gland

• Midbrain (mesencephalon)

• Stays Midbrain and Cerebral Aqueduct

• Hindbrain (rhombencephalon)

• Anterior Metencephalon

• 4th ventricle, cerebellum, and pons

• Posterior Myelencephalon

• 4th ventricle & medulla oblongata


Structure of the Cerebrum

Cerebrum is largest part of brain:

Cerebral hemispheres:

2 halves, separated by falx cerebri

Corpus callosum:

Connects cerebral hemispheres

Gyri:

Ridges or convolutions

Sulci:

Shallow grooves in surface

• Central sulcus.

Fissures:

• Deep grooves in surface.

• Longitudinal: separates the cerebral hemispheres.

• Transverse: separates cerebrum from cerebellum.


Lobes of the Cerebrum

• Frontal lobe

• Parietal lobe

• Temporal lobe

• Occipital lobe

• Insula

4 of the lobes are named for the bones that they underlie.


Structure of the Cerebrum

Cerebral Cortex:

• Thin outermost layer of gray matter

• Contains almost 75% of neuron cell bodies in nervous system.

White Matter of Cerebrum:

• Under cerebral cortex.

• Makes up most of cerebrum.

• Contains bundles of myelinated axons


Functions of the Cerebral Cortex

Cerebral cortex is responsible for higher mental functions:

• Interpreting impulses from sensory organs

• Initiating voluntary movements

• Storing information as memory

• Retrieving stored information

• Reasoning

• Intelligence and personality.


Sensory Areas of the CortexCutaneous sensory area:

• Parietal lobe

• Interprets sensations on skin

Sensory speech area (Wernicke’s area):

• Temporal /parietal lobe

• Usually left hemisphere

• Understanding and formulating language.

Visual area:

• Occipital lobe

• Interprets vision

Auditory area:

• Temporal lobe

• Interprets hearing

Sensory area for taste:

• Near base of the central sulcus

• Includes part of insula

Sensory area for smell:

• Arises from centers deep within temporal lobes.


Association Areas of the Cortex

• Connect to each other and to other structures in the brain

• Widespread in cerebral cortex

• Analyze and interpret sensory experiences

• Provide memory, reasoning, verbalization, judgment, emotions


Association AreasFrontal lobe association areas:

• Concentrating

• Planning

• Complex problem solving

• Emotional behavior, judging consequences of behavior

Parietal lobe association areas:

• Understanding speech

• Choosing words to express thoughts and feelings

Temporal lobe association areas:

• Interpret complex sensory experiences (understanding speech, reading)

• Store memories of visual scenes, music, and complex patterns

Occipital lobe association areas:

• Analyze and combine visual images with other sensory experiences

Insula:

• Translating sensory information into proper emotional responses


Motor Areas of the CortexPrimary motor areas:

• Frontal lobes

• Control voluntary muscles

• Most nerve fibers cross over in brainstem

Broca’s area:

• Anterior to primary motor cortex

• Left hemisphere

• Controls muscles needed for speech

Frontal eye field:

• Above Broca’s area

• Controls voluntary movements of eyes and eyelids

b: © McGraw-Hill Education/Rebecca Gray


Functions of the Cerebral LobesLobe Functions

Frontal lobes Association areas carry on higher intellectual processes for concentrating, planning, complex problem solving, and judging the consequences of behavior.

Motor areas control movements of voluntary skeletal muscles.

Parietal lobes Sensory areas provide sensations of temperature, touch, pressure, and pain involving the skin.

Association areas function in understanding speech and in using words to express thoughts and feelings.

Temporal lobes

Sensory areas are responsible for hearing.

Association areas interpret sensory experiences and remember visual scenes, music, and other complex sensory patterns.

Occipital lobes

Sensory areas are responsible for vision.

Association areas combine visual images with other sensory experiences.


Hemisphere DominanceDominant hemisphere controls:

• Language skills of speech, writing, reading

• Verbal, analytical, and computational skills

Nondominant hemisphere controls:

• Nonverbal tasks

• Motor tasks

• Understanding & interpreting musical and visual patterns

• Provides emotional & intuitive thought processes

*Most people are left hem. dominant


Memory

Short-term (working) memory:

• Neurons connected in a circuit

• Circuit is stimulated over and over

• When impulse flow ceases, memory does also unless it enters long-term memory via memory consolidation (hippocampus directs memory storage to cerebral cortex)

Long-term memory:

• Holds more memory than short-term, lasts a lifetime

• Changes structure or function of neurons

• Enhances synaptic transmission


Basal Nuclei• Sometimes called basal ganglia (technically a ganglion is a cluster of

neuron cell bodies in the peripheral nervous system)

• Masses of gray matter deep within cerebral hemispheres

• Consist of caudate nucleus, putamen, and globus pallidus

• Produce dopamine

• Help control voluntary movement



Parkinson Disease (PD)

• In PD, neurons degenerate in the substantia nigra, which produces the neurotransmitter, dopamine.

• Less dopamine reaches basal nuclei.

• Dopamine deficiency leads to motor problems, such as tremors, shuffling gait, rigidity, small handwriting, speech difficulties, mask-like face.

• No treatments can cure or slow down progression of PD.

• Treated with Levodopa, precursor of dopamine, which can cross blood-brain barrier.

• Surgery and deep brain stimulation have had some success.

• Causes of PD: certain drugs, pesticide exposure, frequent blows to the head.

• There is a genetic component, but it is not directly inherited.


Diencephalon• Between cerebral hemispheres

and above the brainstem

• Surrounds the third ventricle

• Gray matter.

• Structures

• Thalamus

• Hypothalamus

• Optic tracts

• Optic chiasma

• Infundibulum

• Posterior pituitary

• Mammillary bodies

• Pineal gland


DiencephalonThalamus:

• Gateway for sensory impulses ascending to cerebral cortex

• Receives all sensory impulses (except for sense of smell)

• Channels impulses to appropriate part of cerebral cortex for interpretation

Hypothalamus:

• Maintains homeostasis by regulating visceral activities, such as heart rate, blood pressure, body temperature, water & electrolyte balance, hunger, body weight, movement and glandular secretion in digestive tract, sleep and wakefulness, pituitary gland function

• Links nervous and endocrine systems

Limbic System:

• Consists of several structures in various parts of brain, including diencephalon

• Controls emotional responses, feelings, behavior oriented toward survival

• Reacts to potentially life-threatening upsets (physical or psychological)


Brainstem

The Brainstem connects brain to the spinal cord.

Brainstem consists of:

• Midbrain.

• Pons.

• Medulla oblongata.


Midbrain

• Short section of brainstem

• Lies between diencephalon and pons

• Contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain

• Cerebral aqueduct

• Cerebral peduncles (bundles of nerve fibers)

• Corpora quadrigemina (centers for visual and auditory reflexes)

• Red nucleus (role in postural reflexes)


Pons

• Rounded bulge on underside of brainstem

• Between midbrain and medulla oblongata

• Relays nerve impulses between medulla oblongata and cerebrum

• Relays impulses from cerebrum to cerebellum

• Helps regulate rhythm of breathing


Medulla Oblongata

• Enlarged continuation of spinal cord

• Conducts ascending and descending impulses between brain & spinal cord

• Contains cardiac, vasomotor, and respiratory control centers

• Contains various nonvital reflex control centers (coughing, sneezing, swallowing, and vomiting).

• Injuries are often fatal


Reticular Formation• Reticular Activating System

• Network of nerve fibers scattered throughout brain stem

• Extends into the diencephalon

• Connects to centers of hypothalamus, basal nuclei, cerebellum, and cerebrum with ascending and descending tracts

• Filters incoming sensory information

• Arouses cerebral cortex into state of wakefulness

• Decreased activity causes sleep


Types of SleepNon-rapid Eye Movement (Non-R E M) Sleep:

• Slow wave sleep

• Person is tired

• Decreasing activity of reticular formation

• Restful and dreamless

• Reduced blood pressure and respiratory rate

• 3 stages, ranging from light to heavy

• Alternates with R E M sleep

Rapid Eye Movement (R E M) Sleep:

• Paradoxical sleep (because some areas of brain are active)

• Heart and respiratory rates irregular

• Dreaming occurs


Cerebellum• Inferior to occipital lobes

• Dorsal to pons and medulla oblongata

• Two hemispheres separated by falx cerebelli

• Vermis connects hemispheres.

• Cerebellar cortex (gray matter)

• Arbor vitae (white matter)

• Cerebellar peduncles

• Dentate nucleus (largest nucleus)

• Integrates sensory information concerning position of body parts

• Coordinates skeletal muscle activity

• Maintains posture



Brain Waves

• Recordings of fluctuating electrical changes in the brain.

• Commonly recorded from E E G, via electrodes on scalp that detect electrical changes in extracellular fluid of the brain.

• E E G based on potential changes in large groups of neurons.

4 types of brain waves:

• Alpha: awake, resting, eyes closed.

• Beta: active mental activity, under tension.

• Theta: mostly in children.

• Delta: mainly during sleep.

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