Anatomy Quiz Four

Adult brains have four regions:

1. Cerebral hemispheres

2. Diencephalon

3. Brain stem, consisting of:

• Midbrain

• Pons

• Medulla

4. Cerebellum

Brain stem, consisting of : 

• Midbrain

• Pons

• Medulla

Brain stem has additional gray matter ____ scattered within _____ ______.

Brain stem has additional gray matter nuclei scattered within white matter.

Cerebral hemispheres (cerebrum) and cerebellum contain outer layer of ____ _____ called the _____.

Cerebral hemispheres (cerebrum) and cerebellum contain outer layer of gray matter called the cortex.

_______ and ________ also have scattered areas of gray matter nuclei amid white matter.

Cerebrum and cerebellum also have scattered areas of gray matter nuclei amid white matter.

Ventricles

• Fluid-filled chambers that are continuous to one another and to central canal of spinal cord

  • Filled with cerebrospinal fluid (CSF)

Lined by ependymal cells (neuroglial cells)

Cerebral hemispheres

• Form superior part of brain

  • Account for 83% of brain mass

Cerebral hemispheres

Surface markings:

• Gyri: ridges 

• Sulci: shallow grooves 

• Fissures: deep grooves

Longitudinal fissure

Separates two hemispheres

Transverse cerebral fissure

Separates cerebrum and cerebellum

Several sulci divide each hemisphere into five lobes

• Frontal

• Parietal 

• Temporal 

• Occipital

• Insula

• First four are named after overlying skull bones

• Insular lobe is buried under portions of temporal, parietal, and frontal lobes

Cerebral cortex

• is “executive suite” of brain

• the outer layer of the brain, made up of gray matter (neurons and their connections) that covers the cerebrum

• Site of conscious mind : awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding

• Thin (2–4 mm) superficial layer of gray matter

  • Composed of neuron cell bodies, dendrites, glial cells, and blood vessels, but no axons

Functional imaging (PET and MRI) of brain show specific motor and sensory functions are located in discrete cortical areas called domains

Site of conscious mind :

Awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding

Seeing

Hearing

Speaking

Thinking

Four general considerations of cerebral cortex:

1. Contains three types of functional areas:

• Motor areas: control voluntary movement

• Sensory areas: conscious awareness of sensation

• Association areas: integrate diverse information

2. Each hemisphere is concerned with contralateral (opposite) side of body

3. Lateralization (specialization) of cortical function can occur in only one hemisphere

4. Conscious behavior involves entire cortex in one way or another

Cerebral Cortex

• Motor areas 

Located in frontal lobe, motor areas act to control voluntary movement

Cerebral Cortex

• Primary (somatic) motor cortex

• Located in precentral gyrus of frontal lobe

• Pyramidal cells: large neurons that allow conscious control of precise, skilled, skeletal muscle movements

• Pyramidal (corticospinal) tracts: formed from long axons that project down spinal cord 

Somatotopy: all muscles of body can be mapped to area on primary motor cortex

Multimodal association areas

• Receive inputs from multiple sensory areas

• Send outputs to multiple areas

• Allows us to give meaning to information received, store in memory, tie to previous experience, and decide on actions

• Sensations, thoughts, emotions become conscious: makes us who we are

Broadly divided into three parts: anterior association area, posterior association area,and limbic association area

Cerebral Cortex

• Lateralization of cortical functioning

• Lateralization: division of labor between hemispheres

• Cerebral dominance: refers to hemisphere that is dominant for language

  • 90% of humans have left-sided dominance

  • Usually results in right-handedness

  • In other 10%, roles of hemispheres are reversed

Lateralization of cortical functioning (cont.)

• Left and Right Hemisphere

Left hemisphere 

• Controls language, math, and logic

Right hemisphere

• Visual-spatial skills, intuition, emotion, and artistic and musical skills

Hemispheres communicate almost instantaneously via fiber tracts and functional integration

Cerebral White Matter

• Second of the three basic regions of cerebral hemispheres

• Responsible for communication between cerebral areas, and between cortex and lower CNS 

• Consists of myelinated fibers bundled into large tracts 

• Classified according to direction they run:  Association, commissural, and projection fibers

Basal Nuclei (Ganglia)

• Third of the three basic regions of cerebrum

• Each hemisphere’s basal nuclei include a:

  • Caudate nucleus

  • Putamen

    • Caudate nucleus + putamen = striatum

  • Globus pallidus

Functions of basal nuclei(Ganglia) are thought to:

• Influence muscle movements 

• Play role in cognition and emotion

• Regulate intensity of slow or stereotyped movements

• Filter out incorrect/inappropriate responses

• Inhibit antagonistic/unnecessary movements

• Parkinson’s disease and Huntington’s disease are disorders of the basal nuclei

The Diencephalon

Consists of three paired gray-matter structures:

• Thalamus

• Hypothalamus

• Epithalamus

Thalamus

• Bilateral egg-shaped nuclei that form superolateral walls of third ventricle

  • Nuclei project and receive fibers from cerebral cortex

Thalamus

• Main thalamic function

• Is to act as relay station for information coming into cortex

  • Sorts, edits, and relays ascending input such as:

    • Impulses from hypothalamus for regulating emotion and visceral function

    • Impulses from cerebellum and basal nuclei to help direct motor cortices

    • Impulses for memory or sensory integration

• Overall, it acts to mediate sensation, motor activities, cortical arousal, learning, and memory

Hypothalamus

• Located below thalamus

• Forms cap over brain stem 

• Contains many important nuclei

Hypothalamus

• Functions

• The hypothalamus is the main visceral control and regulating center that is vital to homeostasis

•  Chief homeostasis controls:

  • Controls autonomic nervous system

    • Examples: blood pressure, rate and force of heartbeat, digestive tract motility, pupil size

  • Initiates physical responses to emotions

• The hypothalamus also:

  • Regulates body temperature: sweating or shivering

  • Regulates hunger and satiety in response to nutrient blood levels or hormones

  • Regulates water balance and thirst

  • Regulates sleep-wake cycles

  • Controls endocrine system functions such as:

    • Secretions of anterior pituitary gland

    • Production of posterior pituitary hormones

Epithalamus

• Most dorsal portion of diencephalon

• Contains pineal gland (body)  - Secretes melatonin that helps regulate sleep-wake cycle

Brain Stem

• Consists of three regions: midbrain, pons, medulla oblongata

• Controls automatic behaviors necessary for survival

• Contains fiber tracts connecting higher and lower neural centers

Medulla Oblongata

• Respiratory centers

  • Generate respiratory rhythm

  • Control rate and depth of breathing

• Various other centers regulate:

  • Vomiting 

  • Hiccupping 

  • Swallowing 

  • Coughing

  • Sneezing

Cerebellum

• Processes input from cortex, brain stem, and sensory receptors to provide precise, coordinated movements of skeletal muscles

• Also plays a major role in balance

Cerebellar Processing

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 body, as well as visual and equilibrium pathways that:

• Pathways continuously “inform” cerebellum of body’s position and momentum

4. Cerebellar cortex calculates the best way to smoothly coordinate muscle contraction

5. Sends “blueprint” of coordinated movement to cerebral motor cortex and brain stem nuclei

Brain Wave Patterns

• Brain waves reflect electrical activity of higher mental functions

  • Normal brain functions are continuous and hard to measure

Electroencephalogram (EEG)

• Electroencephalogram (EEG) records electrical activity that accompanies brain function

• Electrodes placed on scalp measure electrical potential differences between various cortical areas EEG measures patterns of neuronal electrical activity generated by synaptic activity in cortex

  • Each person's brain waves are unique

• Measures wave frequency in Hertz (Hz), numbers of peaks per second (1 Hz = 1 peak per second)

• Can be grouped into four classes based on Hz:

Alpha, beta, theta,or delta waves

Alpha waves:

(8–13 Hz)—regular and rhythmic, low-amplitude, synchronous waves indicating an “idling” brain

Beta waves:

(14–30 Hz)—rhythmic, less regular waves occurring when mentally alert

Theta waves:

(4–7 Hz)—more irregular; common in children and uncommon in awake adults

Delta waves:

(4 Hz or less)—high-amplitude waves of deep sleep and when reticular activating system is suppressed, as during anesthesia; indicates brain damage in awake adult

Consciousness

• Consciousness involves:

  • Perception of sensation

  • Voluntary initiation and control of movement

  • Capabilities associated with higher mental processing (memory, logic, judgment, etc.)

Classification by Stimulus Type

• Mechanoreceptors

Respond to touch, pressure, vibration, and stretch

Classification by Stimulus Type

• Thermoreceptors

Sensitive to changes in temperature

Classification by Stimulus Type

• Photoreceptors

Respond to light energy (example: retina)

Classification by Stimulus Type

• Chemoreceptors

Respond to chemicals (examples: smell, taste, changes in blood chemistry)

Classification by Stimulus Type

• Nociceptors

Sensitive to pain-causing stimuli (examples: extreme heat or cold, excessive pressure, inflammatory chemicals)

Classification by Location

• Exteroceptors

• Respond to stimuli arising outside body

• Receptors in skin for touch, pressure, pain, and temperature

Classification by Location

• Interoceptors

• Respond to stimuli arising in internal viscera and blood vessels

• Sensitive to chemical changes, tissue stretch, and temperature changes

• Sometimes cause discomfort but usually person is unaware of their workings

Classification by Location

• Proprioceptors

• Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles

• Inform brain of one's movements

Classification by Receptor Structure

• Simple receptors of the general senses

  • General senses include tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense

    • No “one-receptor-one-function” relationship

      • Receptors can respond to multiple stimuli

  • Receptors have either:

    • Nonencapsulated (free) nerve endings or 

    • Encapsulated nerve endings

Thermoreceptors

• Cold receptors are activated by temps from 10 to 40°C

• Located in superficial dermis 

• Heat receptors are activated from 32 to 48°C located in in deeper dermis

• Outside those temperature ranges, nociceptors are activated and interpreted as pain

Nociceptors

Pain receptors triggered by extreme temperature changes, pinch, or release of chemicals from damaged tissue

Muscle spindles

Spindle-shaped proprioceptors that respond to muscle stretch

Tendon organ

Proprioceptors located in tendons that detect Stress

Joint kinesthetic receptors

Proprioceptors that monitor joint position and motion

Endoneurium

Loose connective tissue that encloses axons and their myelin sheaths (Schwann cells)

Perineurium

Coarse connective tissue that bundles fibers into fascicles

Epineurium

Tough fibrous sheath around all fascicles to form the nerve

Most nerves are mixtures of ____ and ____ fibers and ____ and ____ (visceral) fibers

Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers

Nerves are classified according to the ______ they transmit impulses

Nerves are classified according to the direction they transmit impulses

Mixed nerves

• Contain both sensory and motor fibers

• Impulses travel both to and from CNS

Sensory (afferent) nerves:

Impulses only toward CNS

Motor (efferent) nerves

Impulses only away from CNS

Pure _____ (afferent) or ____ ____ (efferent) nerves are rare; most nerves are _____

Pure sensory (afferent) or pure motor (efferent) nerves are rare; most nerves are mixed

Types of fibers in mixed nerves

• Somatic afferent (sensory from muscle to brain)

• Somatic efferent (motor from brain to muscle)

• Visceral afferent (sensory from organs to brain)

• Visceral efferent (motor from brain to organs)

Ganglia

Contain neuron cell bodies associated with nerves in PNS

Vagus nerves

• Only cranial nerves that extend beyond head and neck region

• Most motor fibers are parasympathetic fibers that help regulate activities of heart, lungs, and abdominal viscera

• Sensory fibers carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx

Spinal nerves

• 31 pairs of spinal nerves

• All are mixed nerves named for point of issue from spinal cord

• Supply all body parts except head and part of neck

  • 8 pairs of cervical nerves (C₁–C₈)

  • 12 pairs of thoracic nerves (T₁–T₁₂)

  • 5 pairs of lumbar nerves (L₁–L₅)

  • 5 pairs of sacral nerves (S₁–S₅)

  • 1 pair of tiny coccygeal nerves (C₀)

Sacral plexus

• Arises from L₄ to S₄

• Serves the buttock, lower limb, pelvic structures, and perineum

Sciatic nerve

• Longest and thickest nerve of body

• Innervates hamstring muscles, adductor magnus, and most muscles in leg and foot

• Composed of two nerves: tibial and common fibular

Innervation of Visceral Muscle and Glands

• Autonomic motor endings and visceral effectors are simpler than somatic junctions

• Branches form synapses en passant  (“synapses in passing”) with effector cells via varicosities

• Acetylcholine and norepinephrine act indirectly via second messengers

• Visceral motor responses are slower than somatic responses

Stretch reflex

• Brain sets muscle’s length via stretch reflex

• Example: knee-jerk reflex is a stretch reflex that keeps knees from buckling when you stand upright

• Stretch reflexes maintain muscle tone in large postural muscles and adjust it reflexively

How stretch reflex works

• Stretch activates muscle spindle

• Sensory neurons synapse directly with α motor neurons in spinal cord

• A motor neurons cause extrafusal muscles of
  stretched muscle to contract

Functions of Nervous System