brain - a&p 1

parts of the brain

• cerebrum

• diencephalon

• cerebellum

• brainstem - midbrain, pons, and medulla oblongata

cerebrum

• divided into two hemispheres

• frontal, parietal, occipital, and temporal lobes

• divided by longitudinal fissure

• insula below

gyri

ridge or fold that increases surface area

• precentral gyrus and postcentral gyrus - divided by central sulcus

sulcus

groove that increass surface area

• lateral sulcus (frontal and parietal from temporal), central sulcus (divides frontal lobe from parietal), and parieto-occipital sulcus

what substance makes up the cerebrum?

gray and white matter

gray matter

• composed of soma, dendrites, and unmyelinated axons

  • cortex - superficial layer of gray matter, aka cerebral cortex

  • nucleus - functional group of soma deep in brain

white matter

myelinated axons which grouped together are tracts - makes up most of the brains volume

• projection tracts - connect brain and down into the spinal cord

• commissural tracts - connects the L/R hemispheres and allows for their communication ie corpus callosum

• association tracts - connection regions within a hemisphere

cerebral functions

• sensory - conscious awareness of sensation

• motor - voluntary motor functions

• association - integrate info

  • majority of cerebral cortex

  • receive/send info from/to multiple regions

frontal lobe divisions

• prefrontal cortex - largest association cortex

• precentral gyrus - primary motor cortex - somatic motor

• premotor cortex - motor planning and coordination

prefrontal cortex of frontal lobe

• largest association cortex involved in:

  • planning

  • decision making

  • behavioral regulation

  • self awareness

• fully developed around age 25

precentral gyrus

primary motor cortex that is involved in voluntary movement

motor homunculus

represents proportion of cortex devoted ot each region

broca’s area

• in left frontal lobe

• speech production

  • motor coordination

  • grammatical structure

• broca’s aphasia

brocas aphasia

• cant make speech even though we can understand it. can impact writing and sign language too

  • Patients know what they want to say and understand others, so the condition is very frustrating for them

  • Effects on writing and sign language happen because they are downstream effects of the motor deficit.

phonation

how speech begins - sound made by air passing over the larynx in the respiratory system. Broca’s area coordinates the lips, cheeks, tongue, and facial muscles that turn that sound into intelligible words

grammatical structure

how we link words together to convey meaning

parietal lobe sections:

• parietal association cortex

• postcentral gyrus - primary somatosensory cortex

• somatosensory association cortex

parietal lobe

• mostly association cortex, including some visual association cortex

• Signals flow from sensory receptors along afferent neurons to the primary somatosensory cortex, which then passes them to the association cortex for interpretation

• Tactile memory - recognizing what you’re touching by comparing it with past experience

what is the parietal association cortex involved in?

• spatial awareness - recognizing an object’s position in 3D space

• visual attention - the ability to focus on features like color or shape

what is the postcentral gyrus - primary somatosensory cortex involved in?

general sensation - sits directly posterior to the central sulcus

sensory homunculus

• The body map runs in a specific order from medial to lateral, like the motor homunculus

• The face, mouth, and tongue are drawn large because a big share of the cortex receives sensation from them

• more medial is things like lower half, more lateral is the face and hands

temporal division

• primary auditory cortex

• olfactory cortex

• auditory association cortex

• visual association cortex

• Wernicke’s area

primary auditory cortex

this is the first stop for sound coming from the ears. The olfactory cortex gives conscious awareness of smell

olfactory cortex of temporal division

gives conscious awareness of smell

what happens in the auditory association cortex?

classification of sounds - recognizes sounds, compares them with past experience, and matches them with other stimuli

what happens in the visual association cortex?

visual recognition - recognizes complex visual stimuli, like faces, by pulling together their distinct details

Wernicke’s area

• in the left temporal lobe

• speech comprehension - linking words to symbolic meaning

• Wernicke’s aphasia

wernicke’s aphasia

fluent but nonsensical speech. reaching and writing often severely impaired

• Like Broca’s area, it is usually in the left hemisphere

• It recognizes the sound patterns of words and links them to their meaning

• Patients still have full motor control of speech, but they put words together in ways that don’t make sense

key difference between Broca’s and Wernicke’s aphasia

Wernicke’s patients are often unaware of their disorder. They don’t realize they’re not making sense, get frustrated when others don’t understand them, and feel like other people are the ones not making sense

occipital lobe

• primary visual cortex

• visual association cortex

• Because the eyes are at the front of the head, visual neurons have to travel all the way through the brain to reach the back

primary visual cortex

information to the visual association areas in the parietal and temporal lobes too

what happens in the visual association cortex?

understanding of color, orientation, and shape as well as direction and speed of movement

insula

• vestibular cortex - from inner ear

• gustatory cortex - from tongue

• visceral sensory cortex

• You have to pull back the frontal and temporal lobes to see the insula

• Somatic sensory neurons go to the postcentral gyrus, while visceral sensory

where do somatic sensory neurons go?

to the postcentral gyrus

visceral sensations - controlled by the visceral sensory cortex

• bladder fullness, hunger, nausea, and organ pain

• made possible by x sensory neurons going to the insula

cerebral nuclei

• The three cerebral nuclei are the caudate nucleus, the putamen, and the globus pallidus. They are paired, so there is one set in each hemisphere

• Caudate + putamen + globus pallidus = the basal nucleus

• The basal nucleus is a functional group: gray matter with a shared function, plus the white matter tracts that connect it. It is spread too widely to belong to one lobe

functional group

also called functional brain system, is gray matter with a shared function plus the white matter tracts connecting it. It spreads across too much of the brain to belong to one lobe

• Example: to flex your elbow, the basal nucleus boosts the primary motor cortex neurons for the biceps and suppresses the ones for the elbow extensors

what is a “nucleus” in the CNS?

• a cluster of neuron cell bodies that share a function.

• paired structures - one set in each hemisphere

• it is deep gray matter, unlike the cortex, which is the superficial gray matter

basal nucleus

• The basal nucleus communicates with almost the whole cerebral cortex, the diencephalon, the brainstem, the basal nucleus on the other side, and the premotor cortex.

• control of voluntary movement

  • initiate and execution of voluntary movements

  • inhibit antagonistc or unnecessary movements

• integrate information from multiple brain regions

other roles of the basal nucleus

• procedural learning/muscle memory

• habitual behavior

limbic system parts

• cingulate gyrus

• amygdala

• hippocampus

• connection to olfactory bulb - emotional response to odor, memory formation/retrieval

called the emotional visceral brain

olfactory bulb and the limbic system

not part of the limbic system, but it connects to it. That’s why smells can trigger pleasure or disgust

what connects the two hemispheres?

The corpus callosum

• The cingulate gyrus curves around the corpus callosum. The amygdala sits anterior to the hippocampus

what is the cingulate gyrus (in the limbic system) involved in?

emotional expression through posture, gestures, movements, and facial expressions

what connects the limbic system

The fornix - a white matter tract

how many numbers can the working memory hold?

7-10

memory

encoding, storage, and retrieval of stimuli and information

declarative memory

conscious recollection of facts and knowledge

nondeclarative memory

unconscious performance of things like skills and procedures

consolidation of memory

transfer of info into long term memory due to association, rehearsal, and/or emotion

• prefrontal cortex decides if you keep it or not

• Association example: learning muscles is easier because you already learned the joint actions they work on

• Rehearsal example: reviewing your notes or rewatching the lecture

• Emotion works because the hippocampus is closely tied to the limbic system’s emotional regions, which mark events as important

unified memory

since the hippocampus organized stimuli like this it induces LTP and increases the synaptic activity between associated neurons

• increased dendrite growth and greater NT release

how are memories stored?

in related sensory regions ie sounds in auditory cortex

spatial navigation

• hippocampus processes spatial memories

• forms cognitive map - mental representation of environment

• inc hippocampus grey matter in London taxi drivers

hippocampus and spatial navigation

neurons in the CNS usually don’t divide, but the gray matter of the hippocampus is an exception. It can grow when there’s more demand for spatial processing, and its size can change over time

gustatory cortex - insula

perception of taste

vestibular cortex - insula

conscious awareness of balance

what is the somatosensory association cortex involved in?

integration of stimuli and tactile memory

are there one or two thalamus?

two - paired

Hypothalamus: thermoregulation

• Hypothalamic thermostat

  • Maintains set point/normal range

• Initiates fever

Thalamus information routing

• Info from spinal cord and cranial nerves → sensory reception

• Info from basal nucleus and cerebellum → Regulation of motor cortex activity

• Info from limbic system and hypothalamus → Emotional awareness and responses

Thalamus: info from spinal cord and cranial nerves

Sensory reception

Thalamus: info from basal nucleus and cerebellum

Regulation of motor cortex activity

Thalamus: info from limbic system and hypothalamus

Emotional awareness and responses

Hypothalamus main role

homeostatic control center

• functions include: thermoregulation, food intake, and fluid balance

Hypothalamus other functions

• Endocrine regulation

• Circadian biology and sleep

• Regulation of autonomic nervous system

• Regulation of emotional responses

Hypothalamus: regulation of autonomic nervous system

• Receives sensory input from viscera, limbic system and cerebral cortex

• Regulates ANS centers in brainstem

Hypothalamus: regulation of emotional responses

• Integrates limbic system with cerebrum

  • Perception of emotions

• Integrates limbic system with ANS

  • Visceral responses to emotions

Emotions are generated by

• Limbic system

• Hypothalamus

Sleep and wakefulness overview

• Circadian alerting system

• “Sleep pressure”

• Onset of sleep

• Promotion of wakefulness

Circadian alerting system

• Eyes send photic signal to hypothalamus

• Daytime light exposure

  • Promotes daytime alertness and nighttime drowsiness

• Lower evening light

  • Induces onset of sleep-promoting physiology

Promotion of wakefulness

• Hypothalamus stimulates brainstem

  • In response to circadian pattern, hormones, and stimuli

Sleep stages overview

• Non-rapid eye movement (NREM)

  • Stage 1

  • Stage 2

  • Stage 3

• Rapid eye movement (REM)

Light sleep vs deep sleep

• Light sleep

  • NREM stages 1 and 2

• Deep sleep

  • NREM stage 3

NREM stage 1

• 1-5 min

• Transition into sleep

NREM stage 2

• 10-60 min

• Lower

  • Heart rate

  • Respiratory rate

  • Blood pressure

  • Body temp

• Eye movements stop

REM sleep

• 10-60 min

• Eyes oscillate back and forth

• Heart and respiratory rate increase

• Increased brain activity

  • Limbic system very active, prefrontal cortex is not → strange/intense dreams

• Sleep paralysis

  • Inhibition of voluntary muscular activity

• Consolidation of nondeclarative memories

REM: why dreams are strange/intense

• Limbic system is very active

• Prefrontal cortex is not

Memory consolidation during sleep

• NREM stage 3

  • Declarative memories

• REM

  • Nondeclarative memories

Cerebellum efferent fibers go to

• Cerebrum

• Brainstem

Cerebellum functions

• Motor processing

• Cognitive processing

• Emotional regulation

• Motor/procedural learning

• Language processing

Arteries that supply the brain

• Vertebral arteries

• Internal carotid arteries

Vertebral arteries

• Branch from subclavian

• Travel through vertebral foramina

• Supply cerebellum and posterior cerebrum

• Form basilar artery

Diencephalon parts

• Midline structures hidden by the cerebral hemispheres
• Thalamus (paired)
  • Continuous with brainstem inferiorly
• Hypothalamus: anterior to thalamus
• Epithalamus: posterior to thalamus

Thalamus main role

• “Gatekeeper” to the cerebral cortex
  • All incoming information headed to the cortex passes through the thalamus first
• Edits, sorts, and routes information
  • Edits out unimportant information
  • Groups impulses headed to the same region and sends them on together
• Involved in nearly all cerebral functions

Hypothalamus: thermoregulation

• Hypothalamic thermostat
  • Sets body temperature set point and maintains normal range
  • Control center in feedback loops when temperature deviates
• Initiates fever
  • Resets set point to a higher value

Hypothalamus: food intake

• Monitors
  • Hunger/fullness sensations from the stomach
  • Blood chemistry (nutrient levels)
  • Adipose tissue
• Regulates feelings of hunger/satiety
• Mediates energy expenditure and long-term control of body mass

Hypothalamus: fluid balance

• Balances fluid intake vs. fluid lost to the environment
• Monitors blood osmolarity
  • Concentration of solutes in blood plasma
• Increased osmolarity (dehydration) →
  • Induces thirst through the cerebral cortex
  • Promotes water conservation at kidneys

Hypothalamus: endocrine regulation

• Produces
  • Antidiuretic hormone (ADH): acts on kidneys to regulate water lost as urine
  • Oxytocin: contractile hormone, such as uterine contractions during labor and delivery
• Releases hormones that regulate the pituitary gland
  • Indirectly controls processes the pituitary regulates

Hypothalamus: circadian biology and sleep

• Location of circadian clock: suprachiasmatic nucleus (SCN)
  • Regulates patterns that repeat on a roughly 24-hour cycle
  • Examples: sleep-wake cycles, body temperature, hormone release
• Homeostatic sleep drive
  • “Sleep pressure” increases as wake window increases

Homeostatic sleep drive

• “Sleep pressure” increases as wake window increases
• Promotes drowsiness
• High sleep pressure → transition into sleep

Epithalamus function

• Posterior to thalamus
• Contains the pineal gland
  • Source of melatonin
• Melatonin: circadian effector hormone
  • Changing blood levels send time-of-day information from the brain to the rest of the body
  • Communicator between the circadian clock and body tissues
  • Release timing depends on light; long daylight → shorter melatonin release → affects sleep

Components of emotions

• Sensations
  • Generated by limbic system with hypothalamus
  • Integration of sensory stimuli
  • Cerebral cortex analysis of emotional significance
• Visceral motor responses
• Somatic motor responses
• Cognitive responses

Emotions: visceral motor responses examples

• From limbic system + autonomic control centers
• Involve involuntary muscle and glands
• Examples
  • Blushing (cutaneous vasodilation in cheeks)
  • Crying (lacrimal glands)
  • Racing heart (fear, anger)

Emotions: somatic motor responses examples

• Involve voluntary skeletal muscle
• Examples
  • Frowning, smiling, laughing (muscles of facial expression)
  • Gestures and posture changes

Emotions: cognitive responses

• Conscious recognition, expression, or regulation of emotions
• Example: feeling angry but choosing not to express it

Emotion and memory

• Limbic system (including hippocampus) generates emotional sensations
• Emotion strongly affects what gets encoded into long-term memory

Onset of sleep

• Hypothalamus decreases brainstem communication with thalamus
  • Brainstem relays incoming sensory information; thalamus is the gatekeeper to the cortex
  • “Disconnects” cerebral cortex → no conscious awareness of stimuli like background noise
• Brainstem functions continue
  • Autonomic centers keep regulating breathing and heart rate
• Environmental monitoring continues
  • Very strong or unusual stimuli still pass through, like a smoke alarm

NREM stage 3

• 20-40 min
• Muscles fully relax
• Reduced brain activity
  • Unresponsive to most external stimuli
• Tissue growth and repair processes
  • Growth hormone is released during this stage
  • Example: repairing muscle micro-damage from exercise
• Consolidation of declarative memories

REM: sleep paralysis

• Inhibition of voluntary muscular activity
• Prevents acting out dreams
• Waking suddenly from REM → paralysis can take a few minutes to wear off

Sleep cycle

• One pass through all four stages (NREM 1, 2, 3, and REM)
• Each cycle takes about 1-2 hours
• Usually 4-5 cycles per night
• More time spent in REM with each cycle