Systems Midterm 1

The brain is the most complex object in universe, not close to understanding it

Multiscle entity with interacting changing components at different levels in space and time

Systems neuroscience goal is to describe how multiple elements of nervous system interact to produce behavior

Neuroaxis

Central axis of nervous system, straight in quadrupeds, curved in humans because of brains

Anatomical terms

Rostral/anterior = Front/forward

Caudal/posterior = backwards in animals, backwards of brain/bottom of neuroaxis in humans

Dorsal is top of brain/quadruped body, back of spine

Ventral is bottom of brain/quadruped body, front of spine

Medial is closer to midline, lateral is further from midline

Superior inferior = dorsal, ventral

Proximal distal = trunk vs extremities (fingers distal to wrist)

Sections of brain

Coronal/Frontal = transverse plane, chop off face

Horizontal section = horizontal plane, chop off ear to ear through brain

Sagittal section: split between eyes, sagittal plane

Brain is sectioned

Afferents vs Efferents

Afferents = inputs/upstream

• Neuron 1 is afferent of neuron 2

Efferent = output, downstream

• Neuron 3 is efferent for Neuron 2

Anterograde = normal motion: from cell body to synaptic terminal (orthograde)

Retrograde = reverse motion: from synapse to cell body

Central vs Peripheral

Central = brain + spinal cord

Peripheral Nervous system = cranial + spinal nerves

• Motor + sensory components

• Motor

  • Visceral motor system (Autonomic nervous system)

    • Sympathetic (fight or flight), parasympathetic (rest and digest), enteric (2nd brain in gut) divisions

    • Autonomic ganglia and nerves

  • Somatic Motor system

    • Voluntary, motor nerves

Somatic system

Receptors in skin and muscle

Spinal nerves, contain sensory and motor fibers to skeletal muscles

• Motor nuclei in spinal cord not part of PNS

Sensory Ganglia (not in spinal cord → PNS)

Sensory neuron Cell bodies in dorsal root ganglion

Autonomic Nervous System

Sympathetic System: From thoracic and lumbar vertebrae

Parasympathetic: From cranial and sacral vertebrae

Lower motor nuclei located outside CNS

• Neurons innervating gut, ANS outside spine in PNS

NOTE:
- Autonomic/involuntary behaviors not limited to PNS only

• Knee jerk reflex has spinal neurons

• Somatic/visceral used for PNS only usually, but obviously requires interactions with CNS

Somatic:
- CNS

• Motor afferents, sensory efferents in spinal cord

PNS

• Sensory nerves and ganglia, motor nerves

  • Innervate skeletal muscle

Autonomic

• CNS

  • brain and spinal control of + sensory input from autonomic system

• PNS

  • Symp, para, enteric motor nuclei/nerves

  • Innervate smooth muscle

Brain parts

Forebrain: Cerebrum, Thalamus, BG, HC, Amygdala

• Telencephalon

  • Cortex, nuclei (BG, Amy, BF), lateral ventricles

• Diencephalon

  • HT, thalamus, retina, 3rd ventricle

Midbrain (mesencephalon)

• Superior, inferior collliculi

• Red nucleus

• Substantia nigra

• Cerebral aqueduct

Hindbrain: Pons, Medulla, Cerebellum

• Metencephalon

  • Pons, Cerebellum, 4th ventricle

• Myelencephalon

  • Medulla oblongata, 4th ventricle

Spinal cord + brainstem (central canal): Simple brain, reflexes, fixed patterns for walking,r running

• Add hippocampus, amygdala, can form memories, remember where to get food, predict threats

• Add crotex

  • Learn and reason about more complex situations (env, social network, longer timescales)

Brain thought of as superposition of interconnected sensorimotor loops (short loops + reflex), longer loops (complex memory, prediction)

Ventricles

Ventricles: 4 hollow chambers located in brain, produces CSF along lining, synthesized by ependymal cells which line ventricles

CSF: support weight of brain, protect against shocks, remove metabolic waste by mixing with EC fluid in interstitial spaces during sleep

• Flows from site of production in choroid plexus through various channels and openings to surround brain in subarachnoid space

  • Aqueduct = CSF flows, foreman = hole, cistern = liquid collects, no choroid plexus

1+2 = lateral ventricles,

• Contains 3 horns (anterior, posterior, inferior)

3rd ventricle, 4th ventricle

Meninges

3 membranes surrounding brain

Dura (tough other membrane), arachnoid, pia (thin directly on top of brain)

Arachnoid granulation where CSF interface with blood, exchange metabolites, replenish CSF between dura and pia

Superior sagittal sinus - drains blood from brain, integrates CSF

Subarachnoid space filled with spinal fluid

Hydrocephalus

Water brain

Caused by over secretion of CSF, impaired absorption of CSF via arachnoid granulations, obstruction in ventricle or one of the foramen

Meningitis

Inflammation of meninges

Bacteria pass from blood to space between meninges

Sore throat, fever chills, stiff neck, hate bright light, headache, vomit

Antibitoics otherwise fatal

BBB

Separate circulating blood from brain EC fluids b/c has bacteria, viruses

Brain capillary surrounded by tight junctions, only allow passage of small molecules, also some active transport

• Endothelial cell has intercellular cleft, allows things to diffuse

Allows water, gases O2, CO2, lipid soluble molecules by passive diffusion, Active transport of moeclules like glucose, AA

Prevents large molecules, toxins, bacteria

Circumventricular Organs

brain areas where no BBB, brain blood need to communicate

Subfornical organ - osmoregulation, cardiovascular regulation, energy homeostasis (detects glucose levels, can change behavior)

Area postrema - vomiting

Organum vasculosum (OVLT) detects changes in osmolarity

Areas located close to ventricles, more susceptible to contamination, ventricles can wash out easier

Diencephalon

Thalamus, HT, retina, maxillary bodies

• Massa intermedia connects 2 halves of thalamus

• Thalamus is relay station for senses (not smell)

• Retina grows out of diencephalon

Regulatory, sensory, motor functions

Telencephalon: BG

Projections form parallel loops: Cortex>BG>Thalamus> Cortex

• Pattern repeats in all parts of cortex

Striatum (caudate, putamen, nucelus accumbens), globus pallidus, substantia nigra, pars reticulata

telencephalon: limbic system

ring of structures around diencephalin

Associational functions (memory, learning, emotion, not sensorimotor)

Amygdala, hippocampus, mammillary body, cingulate cortex, fornix, retrosplenial cortex

4 lobes

Frontal (central sulcus), parietal, occipital

Temporal on side, separated from others by lateral/sylvian fissure

Insula

Cortex buried within parietal and temporal lobes, next to lateral sulcus

Associational function, subjective feeling state

Fiber tracts

Ascending (from sensory)

Descending (to motor)

Commisural (contralataeral connections, between hemispheres), myelinated axons

• Corpus callosum

• Anterior commisure

• posterior commisure

• Hippocampal commisure

• Massa intermedia

• Other brainstem sites

Associational (ipsilateral connections within same hemisphere)

• V1 to V2

Some tracts have both components

Human spinal column

All sensory info from body to brain, motor info from brain to skeletal muscles

Also some local processing (reflexes)

Spinal cord only goes 2/3 length of spinal vertebrate column, rest of caudal equina (axons bundles)\

31 pairs of nerves (each go to one side of body)

c4-T1 innervates upper limbs, L2-S3 innervates lower limbs

Dermatomes:
- Skin area innervated by one spinal nerves

Transection through spinal cord

• Gray matter vs white matter distinction

  • Gray matter shaped like H

  • smaller top is dorsal horn,

    • Incoming sensory fibers from receptors in skin, muscle, joints

  • bigger lower H part is ventral horn

    • Exiting motor fibers to muscles

• Surrounded by white axons

• In middle of both H gaps is ventral and dorsal column

  • Ventral = stomach, dorsal = back

Spinal cord organization

Ventral root and dorsal root (motor vs sensory)

Dorsal root ganglion = collection of sensory cell bodies

Motor fibers have their cell bodies located in ventral horn

Dorsal column is all sensory tracts

Surrounding dorsal and ventral horns is both sensory and motor

Spinal nerve

Hetereogenous mixture of both sensory and motor fibers

Sensory fibers not only in skin, but also in muscle tissue (spindles) and in joints (Golgi tendon organs)

• Receptors important for sensing muscle contraction

brainstem

Vital functions (HR, resp)

Sensory, motor, regulatory (ANS, somatic NS) functions

Midbrain, pons, medulla