Lecture 2 Flashcards
Neurotransmitters are used in chemical synapses
where cells are separated by a gap.
When a cell has an action potential
it uses a neurotransmitter to cross the synapse and signal the adjacent cell.
For neuron-to-neuron communication
the effect depends on the receptor and the neurotransmitter.
An excitatory signal stimulates the receiving cell to have its own action potential.
An inhibitory signal inhibits the receiving cell from having an action potential.
The balance of these signals determines whether a cell will initiate an action potential.
Neurotransmitters can be excitatory or inhibitory depending on the receptor in the receiving cell.
Anatomy of the Central Nervous System 🧠
The central nervous system includes the brain and spinal cord.
The brain has a cortex of gray matter and an inner medulla of white matter.
Gray matter consists of cell bodies and some non-myelinated axons.
White matter consists of myelinated axons.
The spinal cord has outer white matter and inner gray matter.
Gray matter in the spinal cord is where connections are made.
White matter in the spinal cord contains axons carrying information to and from the brain.
Parts of the Brain 🧠
The four main parts of the brain are:
Cerebrum
Diencephalon
Brainstem
Cerebellum
Cerebrum and Motor Areas 🧠
The cerebrum is the largest part of the brain and is responsible for thinking.
Motor areas of the cortex send signals to the body to initiate movement.
The primary motor area initiates signals to contract muscles.
Supplementary motor area
frontal eye fields
Most motor areas are located in front of the central sulcus
which divides the frontal and parietal lobes.
Sensory Areas and Somatosensory Cortex 🧠
Sensory areas are involved in receiving information about our surroundings.
Somatosensory cortex deals with touch
temperature
Somato: pertaining to the body.
The primary somatosensory cortex is located in the post-central gyrus.
It receives information from sensory structures throughout the body
mainly from the skin.
Proprioception is the ability to sense the position of body parts in space relative to each other.
Association Areas 🧠
Association areas are regions around the primary sensory cortex that make sense of incoming sensory information.
They interpret the meaning of sensations in terms of what is happening to the body.
Visual Cortex 👁️
The primary visual cortex is located at the back of the occipital lobe.
It receives information from the retina about light and wavelengths.
The brain processes this information to make sense of what we see.
Sensory Areas of the Cerebral Cortex🧠
Visual Processing
Visual information from the retina is transmitted to the occipital lobe.
Visual association area: Located in the occipital lobe. It is responsible for interpreting visual information and putting it in context.
Humans have a large visual association area due to our reliance on visual cues.
Animals that rely more on smell have smaller visual areas compared to humans.
Auditory Processing
Auditory sensory areas: Primarily located in the temporal lobe.
Responsible for processing sounds.
Surrounding regions of the temporal lobe help in making sense of the sounds we hear.
Wernicke’s area:
Processes language and helps us make sense of it.
Broca’s area:
Located in the frontal lobe
it is responsible for language production.
Damage to Broca’s area can impair speech production but not comprehension.
Damage to Wernicke’s area can impair comprehension but not speech production.
Olfactory Processing (Smell) 👃
Olfactory sensory areas: Located in the temporal lobe.
Responsible for our conscious awareness of smells.
Unconscious awareness of smell occurs in other brain regions.
Association of smell and memory is linked to the limbic system.
Example: Smelling a particular soap can trigger memories from the past.
Gustatory Processing (Taste) 👅
Requires looking at the insula
a deeper lobe formed by the folding of the frontal
Anterior insula:
Primarily responsible for taste perception.
Receives information from the tongue regarding salty
sweet
Gustation: Our sense of taste.
Visceral Sensory Processing
Somatosensory areas in the post-central gyrus primarily deal with external sensations.
Visceral sensory:
Sensation of the internal environment.
Involves sensations like tummy discomfort or bladder fullness.
Includes monitoring carbon dioxide levels to regulate breathing.
Conscious perception of viscera also occurs deep in the insula.
Proprioception and Vestibular Sense
Proprioception:
Conscious sense of body position.
Vestibular sense:
Sense of balance.
Inner ears play a role in both hearing and balance.
Perception of head location and movement.
It is debated whether there is a dedicated part of the cerebral cortex for the vestibular sense.
If present
it is located in the posterior region of the insula.
Multimodal Association Areas 🤝
Integration of Sensory Information
Integrate information from multiple senses.
Example: Recognizing something as a duck based on how it sounds and looks.
Involved in pattern recognition
especially faces.
Wernicke’s area also plays a role in understanding language
including contextual cues beyond just the words themselves.
Anterior Multimodal Association Area
Located in the front of the frontal lobe.
Involved in personality
decision-making skills
Fully develops in the mid-20s.
Involved in working memory.
Limbic Association Areas
Related to emotions.
Various parts of the limbic association area will be discussed later in the context of higher brain functions.
🧠 Subcortical Brain Areas
Diving below the cortex
we explore the subcortical areas
⚪ White Matter and Myelinated Axons
White matter consists of myelinated axons
which facilitate fast communication.
Myelination enables rapid transmission of signals. Even non-myelinated axons are fast by certain standards but slower compared to myelinated ones.
These myelinated axons form connections between different areas of the body and brain
as well as between the brain and spinal cord. Bundles of myelinated axons in the central nervous system are called tracts
🧵 Types of White Matter Fibers
There are three types of myelinated axons:
Commissural fibers: Connect the two hemispheres of the brain.
The corpus callosum is the largest example
enabling constant communication between the right and left hemispheres.
Projection fibers: Run up and down
transmitting sensory information to the sensory cortex.
The internal capsule is a major routing area for sensory information traveling to the post-central gyrus.
These fibers also carry motor commands from the brain to the body.
They are organized based on the part of the body they serve
as seen in the sensory homunculus.
Association fibers: Connect gyri within the same hemisphere
facilitating communication between different cortical areas.
For example
visual information can be moved from the visual cortex to association areas for interpretation via these fibers.
🧠 Subcortical Nuclei (Gray Matter Islands)
These are nuclei
the neuron cell bodies
Hippocampus and Amygdala: Part of the limbic system
involved in forming and accessing memories. The amygdala is particularly associated with emotions.
Basal Nuclei: Involved in movement
located around the thalamus.
Caudate Nucleus and Putamen: Form the striatum and are involved in the motivation for movement and social interactions.
Globus Pallidus: Processes information before a decision is made to engage in movement. It’s involved in preventing unwanted movements and in proprioceptive movements.
Subthalamic Nucleus: Located below the thalamus
involved in initiating and stopping tasks.
Substantia Nigra and Movement 🧠
The substantia nigra is a region located lower in the brain
near the brainstem
Parkinson’s Disease
The failure of the substantia nigra to send enough neurotransmitters is linked to diseases like Parkinson’s disease.
Symptoms of Parkinson’s:
Tremors
Difficulty completing tasks
These symptoms are due to a change in the abundance of the neurotransmitter dopamine. In Parkinson’s disease
less dopamine is released than in a healthy neuron.
Treatments for Parkinson’s:
L-Dopa: A synthetic dopamine used to increase dopamine levels in the brain.
When neurons receive less signaling
they may degenerate due to a lack of feedback
Inflammation
especially in the digestive tract (e.g.
Summary of Substantia Nigra
Location: Brainstem
Function: Movement
Issue: Failure to release dopamine leads to Parkinson’s disease
Diencephalon: Connecting the Cerebrum 🧠
The diencephalon is the connection point between the cerebrum and other brain regions
including the brainstem and cerebellum. It is composed of three regions:
Thalamus
Hypothalamus
Epithalamus
Thalamus: The Brain’s Post Office ✉️
The thalamus is a group of nuclei that acts as a main relay station for sensory information. Think of the thalamus as the brain’s main post office. All incoming sensory information is routed through the thalamus before being sent to the appropriate regions of the brain. All senses except smell go through the thalamus.
Examples:
Sense of touch on the left middle finger
→
→ Thalamus
→
→ Somatosensory cortex
Sense of vision
→
→ Thalamus
→
→ Occipital lobe
Sense of taste
→
→ Thalamus
→
→ Insula
The thalamus also performs prioritization
filtering out unnecessary information.
The thalamus plays a role in motor systems and the planning stages of movement. It provides feedback to the motor cortex
influencing whether a movement should be executed.
Hypothalamus: Maintaining Balance ⚖️
The hypothalamus is located below the thalamus and is involved in homeostasis through the endocrine system.
Homeostasis refers to maintaining a stable internal environment in the body.
The hypothalamus receives information from inside and outside the body and responds via homeostasis.
The hypothalamus controls the pituitary gland
which produces hormones that regulate various bodily functions
Examples:
Parathyroid hormone: Acts on bones to pull out calcium
Calcitonin: Acts to remove calcium from the blood
The hypothalamus is also involved with the autonomic nervous system (ANS)
which controls involuntary functions like glands
Autonomic nervous system (ANS) is the automatic functions you are not having to think about with your nervous system
controlling glands and smooth muscles and cardiac muscles.
The hypothalamus controls the autonomic nervous system to maintain bodily balance.
Hypothalamus and Biological Clock ⏰
The hypothalamus contains several nuclei involved in various functions.
Mammillary Bodies: Involved in memory
especially memory associated with smell.
Suprachiasmatic Nucleus: Located above the optic chiasm and receives information from the eyes about the quantity and quality of light. It helps regulate the biological clock.
Biological Clock: The internal mechanism that regulates the sleep-wake cycle and other physiological processes according to a roughly 24-hour rhythm.
Biological Clock Regulation 💡
Our eyes communicate with the suprachiasmatic nucleus
which then communicates with the pineal gland located in the epithalamus.
Pineal Gland: Produces melatonin
a hormone that helps regulate sleep.
Light Spectrum and Melatonin Production 🧪
During the day
we are exposed to broad spectrum light
Red Light: Long wavelength light
Blue Light: Shorter wavelength light
In the evening
we lose light
The eyes report the type of light to the suprachiasmatic nucleus.
If the suprachiasmatic nucleus detects daylight (especially blue light)
it inhibits melatonin production.
When blue light decreases
the pineal gland is signaled to start producing melatonin.
Disruptions to the Biological Clock 💥
Shift Work: Working at night and sleeping during the day disrupts the natural sleep-wake cycle.
Blue Light from Devices: Phones
tablets
Using devices at night can trick the body into thinking it’s daytime.
Doctors recommend turning off screens or using blue light filters to improve sleep.
Health Implications of Biological Clock Disruption 🩺
Exposure to too much blue light at night can lead to:
Sleep problems
Increased risk of cardiovascular disease and diabetes
Early death
Spending time outside
especially at sunrise and sunset
Brain Stem: Connection and Autonomic Behaviors 🧠
The brain stem connects the brain (especially the diencephalon) to the spinal cord.
Functions of the Brain Stem ⚙️
Pathway for motor and sensory impulses
Regulation of autonomic behaviors (e.g.
heart rate
Origin of cranial nerves
Midbrain Structure and Reflexes 👁️👂
The midbrain is the top part of the brainstem. The dorsal side is called the tectum or the roof.
Corpora Quadrigemina: Four lumps on the dorsal side of the midbrain involved in reflexes.
Superior Colliculi: Visual reflexes
Inferior Colliculi: Auditory reflexes
🧠 Midbrain
Inferior colliculi or the lower parts of these corpora quadragemina:
The location of startle reflexes
like being startled by something falling in the bathroom.
Peduncle:
A stalk; where axons travel down from the brain.
Found on the anterior side
indicating motor functions.
Carry motor impulses to innervate muscles.
Anterior part:
Contains big motor tracks carrying information from the brain to move muscles.
Contains nuclei like the substantia nigra and red nucleus.
Substantia nigra:
Involved in motor production and smoothing out muscle actions via dopamine communication between neurons.
Related to Parkinson’s disease.
Red nucleus:
Involved with the movement of limbs.
Other nuclei:
Start of cranial nerves.
Involved in cardiovascular regulation (heart rate) and respiration.
Periaqueductal gray matter:
Located around the central canal.
Involved in pain suppression.
The ventral side (forward side) of the midbrain mainly deals with motor response
while the dorsal side deals with other functions.
🌉 Pons
Connects to the cerebellum.
Axons that wrap around the brainstem to connect to the cerebellum look like “funky 80s haircut with the wings.”
Cerebellum:
Involved in movement and coordination of movement.
Receives plans about how to engage in movement from the brain.
Olives:
Bumps involved in sound processing.
Help determine the direction of a sound source by comparing when the sound reaches each ear.
Contains nuclei of cranial nerves:
Originate in the pons and send axons to control muscles in the head and neck for functions like speaking
chewing
🫀 Medulla Oblongata
The lowest part of the brainstem
a continuation from the midbrain and pons.
Motor axons from the midbrain and pons continue down into the spinal cord through the medulla oblongata.
Posterior side: think sensory information coming up.
Anterior or ventral side: think motor information coming down.
Decussation:
The crossing over of axons.
Most decussation happens in the medulla oblongata.
Commands to contract the right bicep originate in the left side of the brain
and vice versa.
Autonomic control centers:
Located in both the pons and the medulla oblongata.
Control breathing and cardiovascular functions without conscious thought.
Other automatic behaviors controlled include sneezing
coughing
Reticular Activating System (RAS) and Consciousness 🧠
The reticular activating system (RAS)
also known as the reticular formation
It allows sensation to pass through from all of our sensors (touch
temperature
When the RAS is active
it facilitates constant communication with the brain
RAS as Mission Control 🚦
The brain acts as mission control
receiving information from various systems due to the RAS. The RAS works with the autonomic nervous system
The Impact of RAS on Sleep 😴
Sleep is characterized by a lack of consciousness. When we sleep
the RAS stops sending information
Sleep is a lack of consciousness
and is characterized by the reticular activating system not sending information to the brain.
If the RAS doesn’t quiet down
it can be difficult to fall asleep because the brain is constantly receiving sensory input (e.g.
Sleep Stages 🛌
Sleep involves cycles
including REM (Rapid Eye Movement) sleep
There are four levels of sleep characterized by different brain waves. Night terrors and sleepwalking occur during stage four
the deepest part of sleep
Waking Up ⏰
Waking up is initiated by the hypothalamus
which releases a hormone called orexin.
Orexin primes the rest of the systems to start the day
often triggering the release of stress hormones that activate the fight-or-flight system.
People with insomnia often produce too much orexin
which keeps them in a constant state of wakefulness. Researchers are exploring ways to block orexin to help people with insomnia or PTSD fall asleep
