Neurology Overview

Frontal lobe (cerebrum) functions

• Primary motor cortex (voluntary movement)

• Personality

• Speech production (dominant hemisphere for Broca’s area)

Lesions in the frontal lobe will cause

• Personality changes

• Poor judgement

• Contralateral weakness

• Expressive aphasia (impairs speaking, understanding, reading)

Parietal lobe (cerebrum) functions

• Sensory integration

• Spatial awareness

Lesions in the parietal lobe will cause

Sensory loss and neglect especially on the non-dominant side

Temporal lobe (cerebrum) functions

• Hearing

• Memory (hippocampus)

• Language comprehension (Wernicke’s area)

Lesions of the temporal lobe can cause

Receptive aphasia (Wernicke’s area), memory issues, seizures

Occipital lobe (cerebrum) function

Vision

Lesions of the occipital lobe can cause

Visual field defects

The brainstem controls cranial nerves

III-XII

• Heart rate

• Breathing

• Consciousness (RAS)

Neurons purpose

• Sense environment (sensory input)

• Interpret and integrate (CNS) processing

• Respond (motor output)

Neurons receiving signals

Dendrites receive input from other neurons and sensory receptors

Neurons integrating information

Cell body (soma) sums incoming signals

Neurons transmit electrical signals

Action potentials travel down the axon, myelin speeds

• Demyelination (MS, Gullian Bare)→ slowed/blocked conduction

Neurons communicate chemically

At synapse, neurons release neurotransmitters

• Parkinson’s= decreased dopamine

• Depression= altered serotonin

• Seizures= excessive excitatory signal

Sensory (afferent) neurons

Carry info to CNS

• pain, touch, proprioreception

Motor (efferent) neurons

Carry commands from the CNS to muscles or glands

Interneurons

Found in the CNS, connect sensory to motor

• Reflexes, cognition, coordination

Mechanoreceptors (sensory receptors)

Mechanical forces

• Touch, pressure, vibration, stretch, movement

Thermoreceptors (sensory receptors)

temperature changes, cool and warm

Nociceptors (sensory receptors)

extreme mechanical, thermal, chemical

Chemoreceptors (sensory receptors)

Chemical composition (ex. olfactory and taste)

Photoreceptors (sensory receptors)

Light

Exteroreceptors

external stimuli (skin and special senses)

Interoreceptors

Internal environment (BP and pH)

Proprioreceptors

Body position and movement

Brain stem connects

brain to the spinal cord

Brain stem is essential for

autonomic function, CN activity, motor and sensory relay, level of consciousness (RAS)

Midbrain (brainstem)

• Cerebral peduncles: motor pathways

• Superior (visual) colliculi and inferior (auditory) colliculi

• Substantia Nigra: dopamine production

• Red nucleus: motor coordination

• CN III and IV

Pons (brainstem)

• Pontine nuclei: relay to cerebellum

• CN V-VIII

• Respiratory centers

• Ascending and descending tracts

Medulla oblongata (brainstem)

• Pyramids: corticospinal tracts

• Nucleus solitarius: visceral sensory

• Inferior olivary nucleus: motor learning

• CN IX-XII nuclei

• Cardiorespiratory nucleus

Somatic sensory (afferent) pathways

carry conscious sensation from body to brain (pain, temp, touch, vibration)

• DCML

• Spinothalmic tract

• Spinocerebellar tract

Dorsal Column-Medial Lemniscus (DCML) SSP

Fine touch, vibration, proprioreception, pressure

• Ipsilateral loss below lesion

1. Receptor (mechano/prioprioreception)

2. 1st order neuron enters spinal cord

3. Ascend ipsilaterally in dorsal column

4. Synapse in medulla

5. Decussated at the medial lemniscus

6. Thalamus- sensory cortex

Spinothalmic Tract (Anterolateral System) SSP

Carries pain, temperature, crude touch

• Lesion is contralateral pain and temperature loss

1. Free nerve endings

2. 1st order enters spinal cord

3. Synapse immediately

4. Decussates within 1-2 levels

5. Ascends contralaterally

6. Goes from thalamus to cortex

Spinocerebellar Tracts (Unconscious) SSP

Unconscious proprioreception

• Lesions cause ataxia and coordination deficits

1. Muscle

2. Cerebellum (does not reach cortex)

Orders of neurons

1st order: stimuli→ second order neuron

2nd order: brain (thalamus)

3rd order: thalamus→cerebral cortex

Somatic motor (efferent) pathways

UMN→LMN→muscle

• Corticospinal (pyrimidal) tract

Corticospinal (pyramidal) tract

Voluntary movement

1. Motor cortex (frontal lobe)

2. Brainstem

3. decussates at medullary pyramids (medulla oblongata)

4. Synapse in LMN

5. Muscle contraction

Upper motor neuron lesion

Spastic tone, increase reflexes, mild atrophy

Lower motor neuron lesion

Flaccid tone, decrease reflexes, severe atrophy

Stepping on a tack

1. Pain receptor activated

2. Spinothalmic pathway (pain)→ cortex

3. Motor cortex activates (frontal lobe)

4. Corticospinal tract withdrawals foot (voluntary movement)

5. Reflex arc ma bypass cortex for speed

Tracts are

specific kinds of neural pathways

• Ascending (sensory) tracts: sensory information to the brain

• Descending (motor) tracts: motor commands from the brain

DCML tract (ascending)

Fine touch, vibration, proprioreception

• Decussates in medulla (brain stem)

Spinothalmic tract (ascending)

Pain and temperature

• Decussates in spinal cord

Spinocerebellar tract (ascending)

Unconscious proprioreception

• Variable decussation

Corticospinal tract (descending)

Voluntary movement

• Decussates in medulla

Rubrospinal tract (extrapyramidal- descending)

Flexor

Vestibulospinal tract (extrapyramidal- descending)

Balance and extend

Reticulospinal tract (extrapyramidal- descending)

Posture and reflexes

Tectospinal tract (extrapyramidal- descending)

Head and eye coordination

CN locations

• I and II not in brainstem

• III-XII in brainstem

Coverings of the brain

scalp, cranial bone, meninges, CSF

Scalp layers

S- Skin

C- Close subcutaneous tissue

A- Aponeurosis

L- Loose subaponeurotic tissue

P- Pericranium anchored to periosteum

Skull (cranial bone)

Outer table, inner table, endosteum (outer layer of the dura)

Meninges

• Dura mater

  • endosteal and meningeal dura

• Arachnoid mater

• Pia mater

CSF

In arachnoid space and ventricles

• cushioning, nutrient delivery, waste removal

Blood supply to the brain

Internal Carotid A. (front), Vertebral A. (back )

Process of neurotransmission

1. Resting membrane potential maintained by Na/K channels -70 mV

2. Stimulus and graded potentials

3. Action potential generation at threshold -55 mV

4. Propagation of AP (Saltatory conduction)

5. Repolarization

6. Arrival at presynaptic terminal

7. Neurotransmitter release

8. Bind to postsynaptic receptors (nicotinic/muscarinic)

9. Postsynaptic response- EPSP or IPSP

10. Termination of signal- reuptake, enzymatic degradation, diffusion

Nicotinic ACh receptor

Ionotropic (Fast)

Muscarinic ACh receptor

Metabotropic (slow)

Acetylcholine (ACh)

Muscle contraction, autonomic nervous system, memory, hearing

• Location: neuromuscular junction, parasympathetic nervous system, CNS (memory)

• Clinical: low ACh in Alzheimer’s blocked by botulinum toxin

Norepinephrine

Alertness, attention, stress response

• Location: sympathetic nervous system, CNS

• Clinical: low in depression, high in anxiety

Epinephrine

Fight or flight response

• Location: hormonal (adrenal medulla)

• Clinical: used in anaphylaxis or cardiac arrest

Dopamine

Movement, motivation, reward

• Location: Nigrostriatal- movement, Mesolimbic- reward, Mesocortical- cognition, Tuberoinfundibular- prolactin inhibition

• Clinical: low in Parkinson’s, high in psychosis

Serotonin

Mood, sleep, appetite

• Location: Raphe nuclei (cell clusters in brainstem)

• Clinical: low in depression (Target of SSRIs)

GABA (gamma-aminobutryic acid)

Inhibitory NT in CNS

• Clinical: low= seizures (enhanced by benzos and alcohol)

Glutamate

Major excitatory NT for learning and memory

• Clinical: high= excitotoxicity (stroke and TBI)

Glycine

Inhibitory NT

• Location: spinal cord, brainstem

• Clinical: blocked by strychnine

Afferent

Body→ CNS (touch, pain, temp, proprioreception, vision, hearing, taste, smell)

• arrives @ CNS- sensory input

Basic afferent pathway

1. Sensory receptors

2. First order neuron

3. Brainstem/spinal cord (posterior root)

4. Thalamus (2nd order)

5. Primary sensory cortex (3rd order)

KEY: enter spinal cord via dorsal (posterior) root, synapse in dorsal horn

Major afferent tracts

• DCML: fine touch, vibration, proprioreception

• Spinothalmic: pain, temperature, crude touch

• Spinocerebellar: unconscious proprioreception

Efferent

CNS→ body (skeletal, smooth muscle, gland secretion)

• Exits CNS, motor output

Efferent basic pathway

1. Motor cortex/brainstem

2. UMN

3. LMN

4. Effector (muscle or gland)

KEY: Exit spinal cord via the anterior root, cell bodies in ventral horn

Somatic motor (voluntary) efferent pathway

• Skeletal muscle

• Single neuron from CNS→ muscle

• NT=ACh

Autonomic Motor (involuntary) efferent

Smooth muscle, cardiac muscle, glands

• Sympathetic: fight/flight, NE at most target organs

• Parasympathetic: rest/digest, ACh at most target organs

Sympathetic Nervous System (SNS)

Fight or flight, thoracolumbar T1-L2

Parasympathetic Nervous System (PNS)

Rest and digest, craniosacral CN III, VII, IX, X and S2-S4

Upper motor neuron (UMN)

starts in motor cortex/brainstem and descends via corticospinal tract (somatic motor)

• Initiate voluntary movement and modulates reflexes and muscle tone

• Lesion signs (SPASTIC): weakness, spasticity, hyperreflexia, clonus, babinski sign

Lower motor neuron (LMN)

directly innervate skeletal muscle (CNS→ PNS)

• Common pathway for movement and causes muscle contraction

• LMN Lesions: weakness/paralysis, flaccidity, hyporeflexia, muscle atrophy, fasiculations

Neuronal pathways of vision

retina→ visual cortex for conscious vision

1. Retina

2. Optic nerve (CN II)

3. Optic chiasm

4. Optic tract

5. Lateral geniculate nucleus (LGN)

6. Optic radiations (geniculocalcarine)

7. Primary visual cortex

Retina (neuronal pathway of vision)

photoreceptor→ bipolar cells→ ganglion cells (axons form the optic nerve CN II)

Optic nerve (neuronal pathway of vision)

carries visual information from one eye (separated by visual field- nasal vs temporal retina)

Optic chasm (neuronal pathway of vision)

Nasal retinal fibers decussate, temporal do NOT

• each optic tract carries info from contralateral visual field

Optic tract (neuronal pathway of vision)

contains fibers from ipsilateral temporal retina and contralateral nasal retina

• projects mainly to the LGN

Lateral geniculate nucleus (LGN) (neuronal pathway of vision)

thalamic relay nucleus for vision

• organize and refine visual input

• send signals to the visual cortex (occipital lobe via optic radiations)

Optic radiations (geniculocarcine tract)

two major bundles

• Meyer’s loop: superior visual field; lesion is contralateral superior quadrantanopia (pie in the sky)

• Parietal radiations: inferior visual field; lesion is contralateral inferior quadrantanopia (pie on the floor)

Primary visual cortex (neuronal pathway of vision)

located in the occipital lobe along calcarine fissure (deep groove that separates superior and inferior visual fields)

• process orientation, motion, color, and form

Superior visual field

inferior retina

Inferior visual field

superior retina

Temporal visual field

nasal retina

Nasal visual field

temporal retina

Quadrantanopia

Vision loss affecting ¼ of the visual field

Hemianopia

vision loss of ½ of the vision field

• Homonomyoius: same ½ in both eyes

Cerebral edema

excess fluid accumulation in brain tissue leading to increased ICP, decreased cerebral perfusion, risk of herniation

• increase one component, decreased others, increase ICP

Vasogenic edema

breakdown of BBB, extracellular fluid

• Caused by: tumors, abscess, trauma, inflammation

• Image: white matter predominance

• Tx: steroids (dexamethasone)

Cytotoxic edema

Cellular injury (Na/K pump fail)

• Caused by: Ischemic stroke, hypoxia, toxins

• Image: grey and white matter

• NO steroids

Interstitial (hydrocephalic) edema

high CSF pressure→ Transependymal flow

• Caused by: obstructive hydrocephalus

• Image: periventricular white matter

Osmotic edema

Plasma hypo-osmolarity

• Caused by: rapid correction of hyperglycemia or hyponatremia

• fluid shift→ water moves into brain

Signs and symptoms of cerebral edema

Early: headache, N/V, confusion

Late: papilledema, Cushing Triad (hypertension, bradycardia, irregular respirations)

DX of cerebral edema

CT head (non-contrast), MRI

Tx of cerebral edema

elevate head of bed, oxygenation, hypertonic saline or mannitol, underlying cause, steroid (if vasogenic)