Lecture 2 Describing the Brain PDF

Describing the brain and fi nding your way around it What Nervous Systems The nervous system is the body’s complex network responsible for sending, receiving, and interpreting Do? information from all parts of the body. It controls voluntary actions (like moving) and involuntary actions (like...

Describing the brain and fi nding your way around it What Nervous Systems The nervous system is the body’s complex network responsible for sending, receiving, and interpreting Do? information from all parts of the body. It controls voluntary actions (like moving) and involuntary actions (like breathing), while also regulating thoughts, moods, and emotions. Basic Divisions of the Nervous System The central nervous system (CNS)  Composed of the brain and spinal cord.  Responsible for processing information and generating responses. The peripheral nervous system (PNS)  Composed of spinal nerves that branch from the spinal cord and cranial nerves that branch from the brain.  Consists of sensory and motor neurons that connect the CNS to the rest of the body.  Divided into the Somatic Nervous System (controls voluntary movements) and the Autonomic Nervous System (controls involunta Autonomic Nervous System:  Sympathetic (activates "fight or flight" response).  Parasympathetic (restores calm and promotes "rest and digest"). How a Refl ex Works A reflex is a rapid, involuntary response to a stimulus. It involves a simple, automatic pathway that bypasses the brain to save time. Refl ex Arc:  Stimulus (e.g., touching something hot) is detected by sensory receptors.  The sensory neuron sends the signal to the spinal cord.  An interneuron in the spinal cord relays the signal directly to a motor neuron.  The motor neuron activates the appropriate muscles to pull your hand away. Brain The brain is composed of billions of neurons and supporting cells. The brain is a complex organ that controls thought, memory, emotion, touch, motor skills, vision, breathing, temperature, hunger and every process that regulates our body. Parts of Brain Part 1: Brain Directions Part 2: Brain Hemispheres and Lateralization  The cerebrum is divided into two halves: the right and left hemispheres.  They are joined by a bundle of fibers called the corpus callosum that transmits messages from one side to the other.  Each hemisphere controls the opposite side of the body.  Not all functions of the hemispheres are shared.  In general, the left hemisphere controls speech, comprehension, arithmetic, and writing.  The right hemisphere controls creativity, spatial ability, artistic, and musical skills.  Pa r t 3: Lo b e s o f th e B r a i n  The cerebral hemispheres have distinct fissures, which divide the brain into lobes.  Each hemisphere has 4 lobes: frontal, temporal, parietal, and occipital (Fig. 3).  Each lobe may be divided, once again, into areas that serve very specific functions.  Fro n ta l Lo b e :  located right behind your forehead.  It’s the control center for planning, reasoning, and movement.  It’s also involved in personality and decision- making.  If you’re trying to solve a problem or think about the future, you’re using your frontal lobe.  Speech: speaking and writing (Broca’s area)  Body movement (motor strip)  Pa r i e ta l l o b e  located behind the frontal lobe, processes sensory information.  It helps you understand touch, pain, and temperature.  The next time you touch something hot and pull your hand back, you can thank your parietal lobe!  Interprets language, words.  Interprets signals from vision, hearing, motor, sensory and memory.  Spatial and visual perception. O c c i p i ta l l o b e  the occipital lobe, which is the visual processing center. Everything you see is processed here.  Interprets vision (color, light, movement)  Te m p o r a l l o b e  the temporal lobe, located on the sides of your brain, handles auditory information and is critical for memory and language.  Understanding language (Wernicke’s area)  Memory  Hearing  Sequencing and organization Broca’s area Wernicke’s area o lies in the left frontal lobe. If this area is damaged, one may have difficulty moving the tongue or facial muscles to produce the sounds of speech. o The person can still read and understand spoken language but has difficulty in speaking and writing (i.e. forming letters and words, doesn't write within lines) – called Broca's aphasia. Wernicke's area o lies in the left temporal lobe. Damage to this area causes Wernicke's aphasia. The individual may speak in long sentences that have no meaning, add unnecessary words, and even create new words. o They can make speech sounds, however Broca’s Area they have difficulty understanding speech and are therefore unaware of their mistakes. 03 Deep Brain Structur The brain is composed of t h e c e re b r u m , c e re b e l l u m , a n d brainstem Cerebrum: is the largest part of the brain and is composed of right and left hemispheres. It performs higher functions like interpreting touch, vision and hearing, as well as speech, reasoning, emotions, learning, and fine control of movement. Cerebellum: is located under the cerebrum. Its function is to coordinate muscle movements, maintain posture, and balance. Brainstem: acts as a relay center connecting the cerebrum and cerebellum to the spinal cord. It performs many automatic functions such as breathing, heart rate, body temperature, wake and sleep cycles, digestion, sneezing, coughing, vomiting, and swallowing. Cortex o The surface of the cerebrum is called the cortex. o It has a folded appearance with hills and valleys. o The cortex contains 16 billion neurons (the cerebellum has 70 billion = 86 billion total) that are arranged in specific layers. o The nerve cell bodies color the cortex grey-brown giving it its name – gray matter (Fig. 4). Beneath the cortex are long nerve fibers (axons) that connect brain areas to each other — called white matter. o The folding of the cortex increases the brain’s surface area allowing more neurons to fit inside the skull and enabling higher functions. o Each fold is called a gyrus, and each groove between folds is called a sulcus. There are names for the folds and grooves that help define specific brain regions.  Deep  Pathways called white matter tracts connect areas of structures the cortex to each other.  Messages can travel from one gyrus to another, from one lobe to another, from one side of the brain to the other, and to structures deep in the brain.  Hypothalamus: is located in the floor of the third ventricle and is the master control of the autonomic system. It plays a role in controlling behaviors such as hunger, thirst, sleep, and sexual response. It also regulates body temperature, blood pressure, emotions, and secretion of hormones.  Pituitary gland: lies in a small pocket of bone at the skull base called the sella turcica. The pituitary gland is connected to the hypothalamus of the brain by the pituitary stalk. Known as the “master gland,” it controls other endocrine glands in the body. It secretes hormones that control sexual development, promote bone and muscle growth, and respond to stress.  Pineal gland: is located behind the third ventricle. It  Deep structures  Thalamus: serves as a relay station for almost all information that comes and goes to the cortex. It plays a role in pain sensation, attention, alertness and memory.  Basal ganglia: includes the caudate, putamen and globus pallidus. These nuclei work with the cerebellum to coordinate fine motions, such as fingertip movements.  Limbic system: is the center of our emotions, learning, and memory. Included in this system are the cingulate gyri, hypothalamus, amygdala (emotional  Deep structures  Amygdala: which is essential for emotional responses, especially fear. If you’re ever startled, that’s your amygdala kicking in.  Hippocampus: plays a key role in forming new memories. When you learn something new in this class, your hippocampus is working to help you remember it. Cranial nerves  The brain communicates with the body through the spinal cord and twelve pairs of cranial nerves.  Ten of the twelve pairs of cranial nerves that control hearing, eye movement, facial sensations, taste, swallowing and movement of the face, neck, shoulder and tongue muscles originate in the brainstem.  The cranial nerves for smell and vision originate in the cerebrum. the roman numeral, name, and main function of the twelve cranial nerves:  Cells of the brain  The brain is made up of two types of cells: nerve cells (neurons) and glia cells.  Nerve cells  There are many sizes and shapes of neurons, but all consist of a cell body, dendrites and an axon. The neuron conveys information through electrical and chemical signals. A neuron that is excited will transmit its energy to neurons within its vicinity.  Cells of the brain  Neurons transmit their energy, or “talk”, to each other across a tiny gap called a synapse.  A neuron has many arms called dendrites, which act like antennae picking up messages from other nerve cells. These messages are passed to the cell body, which determines if the message should be passed along.  Important messages are passed to the end of the axon where sacs containing neurotransmitters open into the synapse.  The neurotransmitter molecules cross the synapse and  Cells of the brain  Glia cells  Glia (Greek word meaning glue) are the cells of the brain that provide neurons with nourishment, protection, and structural support. There are about 10 to 50 times more glia than nerve cells and are the most common type of cells involved in brain tumors.  Astroglia or astrocytes  are the caretakers — they regulate the blood brain barrier, allowing nutrients and molecules to interact with neurons. They control homeostasis, neuronal defense and repair, scar formation, and also affect electrical impulses.  Cells of the brain  Oligodendroglia cells  create a fatty substance called myelin that insulates axons – allowing electrical messages to travel faster.  Ependymal cells  line the ventricles and secrete cerebrospinal fluid (CSF).  Microglia  are the brain’s immune cells, protecting it from invaders and cleaning up debris. They also prune synapses  Neurochemical Action at Synapses  The communication between neurons primarily occurs at synapses, where neurotransmitters play a key role in transmitting signals. There are two main types of chemical messengers involved in this process: classical neurotransmitters and neuromodulators. Each type influences neuronal activity in distinct ways.  1. Classical Neurotransmission  Classical neurotransmission refers to the direct communication between neurons via neurotransmitters at the synapse. This is the primary  Neurochemical Action at Synapses 1. Classical Neurotransmission Steps in Classical Neurotransmission: 2. Action Potential: When an action potential (electrical signal) reaches the axon terminal of a presynaptic neuron, it triggers the release of neurotransmitters. 3. Release of Neurotransmitters: Voltage-gated calcium channels open, allowing calcium ions to enter the presynaptic neuron. The influx of calcium causes synaptic vesicles containing neurotransmitters (e.g., acetylcholine, glutamate, GABA, dopamine, serotonin) to fuse with the presynaptic membrane. Neurotransmitters are then released into the synaptic  Neurochemical Action at Synapses 1. Classical Neurotransmission Steps in Classical Neurotransmission: 3. Binding to Receptors: Neurotransmitters bind to specific receptors on the postsynaptic neuron’s membrane. This binding either excites (depolarizes) or inhibits (hyperpolarizes) the postsynaptic neuron, depending on the type of neurotransmitter and receptor involved. 4. Termination of Signal: After binding, the neurotransmitters are removed from the synaptic cleft through:  Neurochemical Action at Synapses 1. Classical Neurotransmission Steps in Classical Neurotransmission: Reuptake: The neurotransmitter is taken back into the presynaptic neuron. Enzymatic Degradation: Enzymes break down the neurotransmitter (e.g., acetylcholinesterase breaks down acetylcholine). Diffusion: Neurotransmitters diffuse away from the synapse.  Neurochemical Action at 2. Neuromodulators Synapses Neuromodulators are a subset of neurotransmitter. Neuromodulators differ from classical neurotransmitters in that they do not initiate direct synaptic transmission. Instead, they modulate the activity of neurons over a broader area or longer duration, influencing the general excitability of neural circuits. Characteristics of Neuromodulators: Diffuse Action: Unlike classical neurotransmitters that act on a specific postsynaptic neuron, neuromodulators can influence a larger group of neurons, often through volume transmission (spreading across a wider area). Slow and Sustained Effects: Neuromodulators tend to have a slower onset of action compared to classical neurotransmitters Neurochemical Action at Synapses Modulation of Classical Neurotransmission: They can alter the sensitivity of neurons to classical neurotransmitters, either enhancing or inhibiting the effects of these neurotransmitters.  Neurochemical Action at Synapses Examples of Neuromodulators: Dopamine: In addition to acting as a classical neurotransmitter, dopamine can also act as a neuromodulator, influencing motivation, attention, and learning over longer time scales. Serotonin: Like dopamine, serotonin serves dual roles and can modulate mood, arousal, and overall neural excitability. Endorphins: Act as neuromodulators that reduce pain perception and enhance feelings of pleasure. Norepinephrine (Noradrenaline): Modulates attention, arousal, and stress responses. It can affect the overall alertness and readiness of neural circuits.  Key Diff erences Between Classical Neurotransmitters and Neuromodulators Classical Neuromodulation Neurotransmission Slow and diffuse modulation of neuronal Fast and direct transmission activity Affects larger areas of the brain or entire Acts on specific synapses systems Immediate effects on postsynaptic Prolonged effects on the excitability of neurons neurons Short-lasting effects Long-lasting effects Involves neurotransmitters like Involves chemicals like dopamine, acetylcholine, GABA, and glutamate serotonin, norepinephrine THANK YOU!