bio241 lecture 8 a/b/c/d

What are the general characteristics of the CNS?

Consists of brain and spinal cord

• brain is largest and most complex portion of nervous system

• Brain controls sensation, perception, movement, thinking

• Brain consists of 2 cerebral hemispheres, diencephalon, brainstem, cerebellum

• Brainstem connects brain to spinal cord

• Brain and spinal cord connect to the PNS by peripheral nerves

What is the meninges?

Membranes that protect brain and spinal cord; lie between bone and soft tissues of nervous system

• consists of Dura mater, Arachnoid mater, Pia mater

What is the dura mater?

Outer layer

• tough, dense connective tissue

• Dural sinuses

• Epidural space

What is the arachnoid mater?

Middle layer, web-like

• subarachnoid space contains CSF

What is the pia mater?

Inner layer, attached to surface of brain, spinal cord

• contains blood vessels and nerves

• Nourishes CNS

What are the properties of the ventricles?

Produces CSF; interconnected cavities within cerebral hemispheres and brainstem

• ventricles are continuous w/ the central canal of the spinal cord

• 2 lateral ventricles (first and second), third, fourth ventricle

What is the interventricular foramina?

Connect third to lateral ventricles

What is the cerebral aqueduct?

Connects third and fourth ventricles

What are the properties of CSF?

Produced by the choroid plexuses

• selective transfer of substances from the blood to form CSF

• Nutritive and protective of CNS neurons

• Helps maintain stable ionic concentrations in the CNS

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

• Vol is about 140mL

What is a TBI?

Traumatic brain injury→ result of mechanical force such as a fall, attack, accident, sports injury

What is a concussion?

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

What is a CTE?

Chronic traumatic encephalopathy→ 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

What is a blast-related brain injury?

Severe TBI, results from explosions in combat situations; often leads to cognitive decline years after injury

What is the purpose of CSF pressure?

Continuous secretion/reabsorption of CSF keeps fluid pressure in ventricles constant

• interference w/ circulation can increase intracranial pressure in ventricles

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

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

What is used to measure CSF pressure?

Spinal tap/lumbar puncture

What are the functions of the brain?

1. Neural centers for sensory function

2. Sensations and perceptions

3. Motor commands to skeletal uncles

4. Higher mental functions, such as memory, reasoning

5. Neural centers for coordinating muscular movement

6. Neural centers for regulating visceral activities

7. Personality

What are the major regions of the adult brain?

1. Cerebrum

2. Diencephalon

3. Cerebellum

4. Brainstem

• midbrain

• Pons

• Medulla oblongata

What are the properties of the cerebrum?

Largest part of brain→ 2 hemispheres

1. Corpus callosum→ connects cerebral hemispheres

2. Gyri→ ridges or convolutions

3. Solci→ shallow grooves in surface

4. Fissures→ deep grooves in surface

• longitudinal: separates cerebral hemispheres

• Transverse→ separates cerebrum from cerebellum

What are the 5 lobes of the cerebrum?

1. Frontal lobe

2. Parietal lobe

3. Temporal lobe

4. Occipital lobe

5. Insula (deep within lateral sulcus)

What is the cerebral cortex?

Thin layer of gray matter that makes up outermost layer of all outer lobes of the cerebrum

• contains almost 75% of neuron cell bodies in nervous system

What is the white matter of the cerebrum?

Lies under cerebral cortex

• makes up most of cerebrum

• Contains bundles of myelinated axons that connect neuron cell bodies in cerebral cortex to other portions of nervous system

What are the functions of the cerebral cortex?

1. Interpreting impulses from sensory organs

2. Initiating voluntary movements

3. Storing information as memory

4. Retrieving stored info

5. Reasoning

6. Seat of intelligence and personality

• divided into sensory, association, and motor areas (w/ overlap)

What is the function of the frontal lobes?

1. Association areas→ intellectual processes for concentrating, planning, complex problem solving, and judging consequences of behavior

2. Motor areas→ control movements of voluntary skeletal muscles

What is the function of the parietal lobes?

1. Sensory areas→ provide sensation of temp, touch, pressure, pain involving skin

2. Association areas→ understanding speech and using words to express thoughts and feelings

What is the function of the temporal lobes?

1. Sensory areas→ responsible for hearing

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

What are the properties of the occipital lobes?

1. Sensory areas→ vision

2. Association areas→ combine visual images w/ other sensory experiences

What hemisphere is more dominant?

Left cerebral hemisphere

What does the dominant hemisphere control?

1. Language skills of speech, writing, reading

2. Verbal, analytical, computational skills

What does the nondominant hemisphere control?

1. Nonverbal tasks

2. Motor tasks involving orientation in space

3. Understanding and interpreting musical and visual patterns

4. Provides emotional and intuitive thought processes

What is memory?

Consequence of learning and involves persistence of learning

• short-term (working) memory

• Long-term memory

What is short-term (working) memory?

Neurons connected in a circuit

Circuit is stimulated over and over

When impulse flow ceases, memory also ceases, unless it enters long-term memory via memory consolidation

What is long-term memory?

Holds memory for a life-time

• changes structure or function of neurons, making new synaptic connections by increasing branching of processes

• Long-term potentiation

What is long-term potentiation?

Increase in neurotransmitter release and effectiveness of synaptic transmission upon repeated stimulation

What are the properties of the diencephalon?

Between cerebral hemispheres and above brainstem

• surrounds third ventricle, composed of gray matter

Contains:

1. Thalamus

2. Hypothalamus

3. Optic tracts

4. Optic chiasmata

5. Infundibulum

6. Posterior pituitary

7. Mammillary bodies

8. Pineal gland

What is the function of the thalamus?

Gateway for sensory impulses ascending to cerebral cortex

• receives all sensory impulses except smell

• Channels impulses to appropriate part of cerebral cortex for interpretation

What is the function of the hypothalamus?

Maintains homeostasis by regulating visceral activities

Ex. Blood pressure, heart rate, temp, water/electrolyte balance, hunger, body weight, movement and glandular secretion, etc.

• links nervous and endocrine systems

What is the function of the 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)

What are the properties of the brainstem?

Connects brain to spinal cord

• midbrain, pons, medulla oblongata

• Connects nerve fiber tracts and gray matter masses

What are the properties of the 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 info for proprioception

• Coordinates skeletal muscle

• Maintains posture

What is an EEG?

Electroencephalogram→ electrode on scalp that detect electrical changes in ECF of the brain

What are the 4 types of brain waves?

1. Alpha

2. Beta

3. Theta

4. Delta

What do delta waves indicate?

Mainly present during sleep

What do theta waves indicate?

Present in mainly in children, or sleeping/stressed adults

What do beta waves indicate?

Active mental activity under tension

What do alpha waves indicate?

Awake, resting, eyes closed

What is the spinal cord?

Slender column of nervous tissue continuous with brain and brainstem

• extends downward through vertebral canal

• Begins at foramen magnum I and terminates at first and second lumber vertebrae space

• Consists of 31 segments→ pair of spinal nerves

• Within each group, there is a superior/inferior

What does the cervical enlargement supply?

Supplies nerves to upper limbs

What does the lumbar enlargement supply?

Supply nerves to lower limbs

What does the conus medullaris supply?

Tapering region below lumbar enlargement

What is the filum terminale?

Cord of connective tissue that anchors spinal cord to coccyx

What is the cauda equina?

Group of lumbar and sacral nerves extending downward from conus medullaris in vertebral canal

What is the structure of the spinal cord?

1. Anterior median fissure and posterior median sulcus→ grooves that extend whole length of spinal cord

• white matter surrounds gray matter

• Gray matter arranged in horns

• White matter arranged in funiculi

• Posterior roots contain sensory neurons

• Anterior roots contain motor neurons

What are the functions of the spinal cord?

1. Center for spinal reflexes

2. Conduit for impulses to and from the brain

What is a reflex?

Automatic, subconscious response to a stimuli within or outside the body

• maintain homeostasis by controlling involuntary processes, such as heart rate, blood pressure, swallowing, coughing

What is the reflex arc?

Neural pathway, consisting of a sensory receptor, 2 or more neurons, and an effector

What does a simple reflex arc contain?

Only sensory and motor neurons

What does the common reflex arc contain?

Sensory neuron, interneurons, motor neurons

What is the process of a reflex arc?

1. Receptor senses impulse from stimulus→ cell body electronically changes, sending an impulse

2. Impulse is sent through interneuron to the posterior horn of the spinal cord

3. Impulse travels to brain, where it sends a signal down a descending pathway through the anterior horns of the spinal cord to an effector

4. Effector acts upon motor impulse

What is a monosynaptic (stretch) reflex?

Contains 2 neurons→ sensory and motor

• only 1 synapse in spinal cord

• Helps maintain an upright posture

What is an example of a stretch reflex?

Patellar/knee-jerk reflex

What is a withdrawal reflex?

Occurs hen person touches or steps on something painful

• prevents or limits tissue damage by removing limb from painful stimulus

• Polysynaptic: contains sensory, interneuron, and motor neuron

• Reciprocal innvervation: flexors contract, extensors inhibited

What is the process of the patellar reflex?

1. Tapping the patellar ligament sends the motion through the patella into the quad muscles

2. Sensory neurons innervating the quad muscle senses impulse, sending a signal up an ascending pathway to spinal cord

3. Spinal cord receives impulse via sensory neuron of the posterior horn, sends impulse back through the anterior horns

4. Impulse travels down a descending pathway back to quad muscle via motor neuron

5. Motor neuron controls quad muscle (effector) to contract, causing kick reaction

What is the process of the withdrawal reflex?

1. Pain felt by pain Receptor of the foot→ sends signal to sensory neuron

2. Sensory neuron sends impulse up an ascending pathway the posterior horns of the spinal cord

3. Spinal cord receives impulse and converts it into a motor impulse through the anterior horns

4. Anterior horn sends signal down a descending pathway to effector

5. Effector muscles contracts, taking limb away from pain source

What is the crossed extensor reflex?

1. During withdrawal reflex, flexors on affected (ipsilateral) side contract and extensors are inhibited

2. At same time, extenors on opposite (contralateral) side contract, flexors inhibited

3. Also shifts body weight, so person remains upright

What is an ascending tract?

Conduct impulses to the brain

What is a descending tract?

Conduct motor impulses from the brain via motor neurons reaching muscles and glands

What are the major ascending spinal cord tracts?

1. Fasciculus gracilis and fasciculus cunneatus

2. Spinothalamic tracts

3. Spinaocerebellar tracts

What are the major descending (motor) spinal cord tracts?

1. Corticospinal tracts

2. Reticulospinal tracts

3. Rubrospinal tracts

What is the function of the fasciculus gracilis/cuneatus tract?

Located: posterior funiculi

• conduct sensory impulses associated w/ senses of touch, pressure, and body movement from skin, muscles, tendons, and joints to brain

What is the function of the spinothalmic tracts (posterior/anterior)?

Located: lateral and anterior funiculi

• conduct sensory impulses associated w/ senses of pain, temp, touch, and pressure form various body regions to brain

What is the function of the spinocerebellar tract (posterior/anterior)?

Located: lateral funiculi

• conduct sensory impulses for the coordination of muscle movements from muscle of the lower limbs and trunk to the cerebellum

What is the function of the corticospinal tracts (lateral/anterior)?

Located: lateral and anterior funiculi

• conduct motor impulses associated w/ voluntary movements from the brain to the skeletal muscles

What is the function of the reticulospinal tracts (lateral, anterior, medial)?

Located: lateral and anterior funiculi

• conduct motor impulses associated w/ the maintenance of muscle tone and activity of sweat glands from the brain

What is the function of the rubrospinal tract?

Located: lateral funiculi

• conduct motor impulses associated w/ muscular coordination from the brain

What is amyotropic lateral sclerosis (ALS)?

Motor neuron disease

• involves degeneration of motor neurons in spinal cord, brainstem, cerebral cortex

• possible causes: overactive microglia that’s kill neurons, or buildup of oxygen-free radicals that neurons or astrocytes cannot counter

• cognitive function is normal

• Fatal in 2-5 years due to respiratory problems

What are the properties of the peripheral nervous system?

Consists of cranial and spinal nerves

• contains somatic nervous system, autonomic nervous system

What is the somatic nervous system?

Cranial and spinal nerves connect CNS to the skin and skeletal muscles (voluntary)

What is the autonomic nervous system?

Cranial and spinal nerves that connect CNS to viscera (involuntary activities)

What are sensory nerves?

Conduct impulses into brain or spinal cord

What are motor nerves?

Conduct impulses to muscles or glands

What are mixed nerves?

Contain both sensory and motor nerve fibers

• all spinal nerves are mixed (except first pair)

How many cranial nerves are there?

12 pairs of nerves

Whati is CN1?

Olfactory nerve (sensory)

• sensory fibers conduct impulses associated w/ sense of smell

What is CN2?

Optic nerve (sensory)

• sensory fibers conduct impulses associated w/ sense of vision

What is CN3?

Oculomotor (motor)

• motor fibers conduct impulses to muscles that raise eyelids, move eyes, adjust amount of light entering eyes, focus lense

• Some sensory fibers associated w/ proprioceptors

What is CN4?

Trochlear (motor)

• motor fibbers conduct impulses to muscles that move eyes

• Some sensory fibers conduct impulses associated w/ proprioception

What is CN5?

Trigeminal (mixed)

1. Ophthalmic→ sensory fibers conduct impulses from surface of eyes, tear glands, scalp, and upper eyelids

2. Maxillary→ sensory fibers conduct impulses from scalp, skin of jaw, lower teeth, gum, lip

3. Mandibular→ conduct impulses to muscles of mastication and muscles of the floor of the mouth

What is CN6?

Abducens (motor)

• motor fibers conduct impulses to muscles that move eyes

• Sensory fibers conduct impulses associated w/ proprioceptors

What is CN7?

Facial (mixed)

• sensory fibers conduct impulses associated w/ taste receptors of anterior tongue

• Motor fibers conduct impulses to muscles of facial expression, tear glands, and salivary glands

What is CN8?

Vestibulocochlear (sensory)

• sensory fibers conduct impulses associated w/ sense of equilibrium

• Sensory fibers conduct impulses associated w/ sense of hearing

What is CN9?

Glossopharyngeal (mixed)

• sensory fibers conduct impulses from the pharynx, tonsils, posterior tongue, and carotid arteries

• Motor fibers conduct impulses to salivary glands and to muscles of the pharynx used on swallowing

What is CN10?

Vagus (mixed)

• sensory fibers conduct impulses from the pharynx, larynx, esophagus, and viscera of the thorax and abdomen

• Somatic motor fibers conduct impulses to muscles associated w/ speech and swallowing

• Autonomic motor fibers conduct impulses to the viscera of the thorax and abdomen

What is CN11?

Accessory (motor)

• motor fibers conduct impulses to muscles of the soft palate, pharynx, and larynx

• Motor fibers conduct impulses to muscle of neck and back (some proprioceptor input)

What is CN12?

Hypoglossal (motor)

• motor fibers conduct impulses to muscles that move the tongue; some proprioceptor input

How many cervical nerves are there?

8

How many thoracic nerves are there?

12

How many lumbar nerves are there?

5

How many sacral nerves are there?

5

What does Co stand for?

Coccygeal nerve

What is a dermatome?

Area of skin innervated by sensory nerve fibers of a particular spinal nerve (below C1)